GNU Coreutils

https://www.gnu.org/software/coreutils/manual/
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### chmod examples: set permissions

Source: https://www.gnu.org/software/coreutils/manual/html_node/chmod-invocation.html

Examples that set file permissions to world-readable and user-writable, using numeric and symbolic modes.

```bash
# Change file permissions of FOO to be world readable
# and user writable, with no other permissions.
chmod 644 foo
chmod a=r,u+w foo

```

--------------------------------

### timeout examples with signals and kill-after

Source: https://www.gnu.org/software/coreutils/manual/html_node/timeout-invocation.html

Four example invocations showing default TERM signal, custom INT signal, handling of ignored signals, and using --kill-after to force KILL. Each example includes comments explaining expected behavior and exit status.

```bash
# Send the default TERM signal after 20s to a short-living 'sleep 1'.
# As that terminates long before the given duration, 'timeout' returns
# with the same exit status as the command, 0 in this case.
timeout 20 sleep 1

```

```bash
# Send the INT signal after 5s to the 'sleep' command.  Returns after
# 5 seconds with exit status 124 to indicate the sending of the signal.
timeout -s INT 5 sleep 20

```

```bash
# Likewise, but the command ignoring the INT signal due to being started
# via 'env --ignore-signal'.  Thus, 'sleep' terminates regularly after
# the full 20 seconds, still 'timeout' returns with exit status 124.
timeout -s INT 5s env --ignore-signal=INT sleep 20

```

```bash
# Likewise, but sending the KILL signal 3 seconds after the initial
# INT signal.  Hence, 'sleep' is forcefully terminated after about
# 8 seconds (5+3), and 'timeout' returns with an exit status of 137.
timeout -s INT -k 3s 5s env --ignore-signal=INT sleep 20

```

--------------------------------

### ln examples: bad and better practices

Source: https://www.gnu.org/software/coreutils/manual/html_node/ln-invocation.html

Provides contrasting examples of using `ln -s`. The bad examples show creating a link that points to itself and using hard-coded file names. The better examples demonstrate changing to the target directory first and using relative file names to survive directory moves and work across networked file systems.

```shell
Bad Example:

# Create link ../a pointing to a in that directory.
# Not really useful because it points to itself.
ln -s a ..

Better Example:

# Change to the target before creating symlinks to avoid being confused.
cd ..
ln -s adir/a .

Bad Example:

# Hard coded file names don't move well.
ln -s $(pwd)/a /some/dir/

Better Example:

# Relative file names survive directory moves and also
# work across networked file systems.
ln -s afile anotherfile
ln -s ../adir/afile yetanotherfile

```

--------------------------------

### mkdir -p with umask example

Source: https://www.gnu.org/software/coreutils/manual/html_node/mkdir-invocation.html

Example from the -p option description: using a subshell with umask to control parent directory permissions when creating P/Q.

```bash
(umask u=rwx,go=rx; mkdir -p P/Q)

```

--------------------------------

### basename examples

Source: https://www.gnu.org/software/coreutils/manual/html_node/basename-invocation.html

Examples demonstrating basename usage: stripping directory and suffix, using -s, and using -a with multiple names.

```shell
# Output "sort".
basename /usr/bin/sort

# Output "stdio".
basename include/stdio.h .h

# Output "stdio".
basename -s .h include/stdio.h

# Output "stdio" followed by "stdlib"
basename -a -s .h include/stdio.h include/stdlib.h

```

--------------------------------

### join example with two input files

Source: https://www.gnu.org/software/coreutils/manual/html_node/join-invocation.html

Example showing the contents of file1 and file2 and the output of 'join file1 file2'. The output lines consist of the join field, the remaining fields from file1, then the remaining fields from file2.

```text
$ cat file1
a 1
b 2
e 5

```

```text
$ cat file2
a X
e Y
f Z

```

```text
$ join file1 file2
a 1 X
e 5 Y

```

--------------------------------

### install synopses

Source: https://www.gnu.org/software/coreutils/manual/html_node/install-invocation.html

Four usage patterns for the install command: copying a single source to a destination, copying multiple sources to a directory, using the -t option to specify a target directory, and using -d to create directories.

```shell
install [option]... [-T] source dest
install [option]... source... directory
install [option]... -t directory source...
install [option]... -d directory...

```

--------------------------------

### Bad example: ln -s $(pwd)/a /some/dir/

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows a bad example using hard-coded file names that don't move well.

```shell
# Hard coded file names don't move well.
ln -s $(pwd)/a /some/dir/
```

--------------------------------

### Unit separator examples for --unit-separator option

Source: https://www.gnu.org/software/coreutils/manual/html_node/numfmt-invocation.html

Shows example invocations of the --unit-separator option to control the separator between numbers and units. The examples demonstrate adding a space on output, disabling blanks on input, supporting blanks on input via --delimiter, and outputting a non-breaking space.

```text
Add a space on output: --unit-separator=' '
Disable blanks on input: --unit-separator=''
Support blanks on input: --delimiter=''
Ditto and output non-breaking space: -d '' --unit-separator=$'\u00A0'

```

--------------------------------

### touch --date example with timezone

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows the GNU extension syntax for the --date option, allowing a space instead of 'T' and including timezone offsets. The example specifies a timestamp with nanosecond precision.

```shell
--date="2020-07-21 14:19:13.489392193 +0530"
```

--------------------------------

### Simple tsort example with input and output

Source: https://www.gnu.org/software/coreutils/manual/html_node/tsort-invocation.html

A basic example using a here-document to provide input pairs to tsort. The input defines a partial ordering, and the output shows the resulting total ordering.

```text
tsort <<EOF
a b c
d
e f
b c d e
EOF

```

```text
a
b
c
d
e
f

```

--------------------------------

### chmod examples: add execute permissions

Source: https://www.gnu.org/software/coreutils/manual/html_node/chmod-invocation.html

Examples that add user and group execute permissions using numeric and symbolic modes.

```bash
# Add user and group execute permissions to FOO.
chmod +110 foo
chmod ug+x foo

```

--------------------------------

### chgrp examples

Source: https://www.gnu.org/software/coreutils/manual/html_node/chgrp-invocation.html

Two examples from the Examples section. The first changes the group of /u to "staff". The second changes the group of /u and its subfiles to "staff" using the -h and -R options.

```bash
# Change the group of /u to "staff".
chgrp staff /u
```

```bash
# Change the group of /u and subfiles to "staff".
chgrp -hR staff /u
```

--------------------------------

### df --output examples

Source: https://www.gnu.org/software/coreutils/manual/html_node/df-invocation.html

Examples showing how to use the --output option to select specific fields. The first prints the target mount point along with block and inode percentages; the second prints all available fields using the abbreviated --o form.

```shell
#!/bin/sh
# Print the TARGET (i.e., the mount point) along with their percentage
# statistic regarding the blocks and the inodes.
df --out=target --output=pcent,ipcent

# Print all available fields.
df --o

```

--------------------------------

### printf conversion specifier examples

Source: https://www.gnu.org/software/coreutils/manual/html_node/printf-invocation.html

A table of conversion specifiers with shell format examples and their corresponding outputs, illustrating the behavior of each specifier.

```shell
CONVERSION  Shell format example        Output

%s          '[%10s]' 'left pad'         [  left pad]
%s          '[%-10s]' 'right pad'       [right pad ]
%c %s       '%c %.3s' un unibyte        u uni

%d %i       "%'d ;%04i" 1234 '-1'       1,234 ;-001
%o          '%#o' $((2#110100100))      0644
%u          '%u' 0xFFFFFFFF             4294967295
%x          '0x%08x' 11259375           0x00abcdef

%a %f       '%1$a %1$f' 0.0009765625    0x8p-13 0.000977
%e %f       '%1$e %1$f' 123.456789      1.234568e+02 123.456789
%g          '%1$g %1$.2g' 1.2345678e3   1234.57 1.2e+03

%b          '%bfoo' 'bar\cbaz' qux      bar
%q          '%q ' 'a' \;b $'c\n'        a ';b' 'c'$'\n'

```

--------------------------------

### mv -T --exchange example

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Example of using mv with --exchange and --no-target-directory to exchange two directories D1 and D2. This avoids confusion about the destination location.

```shell
mv -T --exchange D1 D2
```

--------------------------------

### Bad example: ln -s a ..

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows a bad example of creating a symlink that points to itself, which is not useful.

```shell
# Create link ../a pointing to a in that directory.
# Not really useful because it points to itself.
ln -s a ..
```

--------------------------------

### Create and enter a directory for csplit exercise

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Creates an empty directory 'd' and changes into it, as a prerequisite for the csplit usage example.

```shell
$ mkdir d && cd d
```

--------------------------------

### paste: Example input files num2 and let3

Source: https://www.gnu.org/software/coreutils/manual/html_node/paste-invocation.html

Sample input files used in the examples: `num2` contains numbers 1 and 2, `let3` contains letters a, b, and c.

```bash
$ cat num2
1
2
$ cat let3
a
b
c

```

--------------------------------

### Example /etc/passwd line

Source: https://www.gnu.org/software/coreutils/manual/html_node/The-cut-command.html

Shows the colon-separated fields of a /etc/passwd entry, used as input for the cut examples.

```text
arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash

```

--------------------------------

### Example Debian version strings

Source: https://www.gnu.org/software/coreutils/manual/html_node/Hyphen_002dminus-and-colon.html

List of valid Debian version strings illustrating the syntax, including optional epoch and debian_revision parts.

```text
60.7.2esr-1~deb9u1
52.9.0esr-1~deb9u1
1:2.3.4-1+b2
327-2
1:1.0.13-3
2:1.19.2-1+deb9u5

```

--------------------------------

### cat examples: concatenate files and standard input

Source: https://www.gnu.org/software/coreutils/manual/html_node/cat-invocation.html

Two examples: output f's contents, then standard input, then g's contents; and copy standard input to standard output.

```text
# Output f's contents, then standard input, then g's contents.
cat f - g

```

```text
# Copy standard input to standard output.
cat

```

--------------------------------

### Run uptime and show output

Source: https://www.gnu.org/software/coreutils/manual/html_node/uptime-invocation.html

Example of running the `uptime` command and its typical output, showing current time, uptime, number of users, and load averages.

```shell
$ uptime
 14:07  up   3:35,  3 users,  load average: 1.39, 1.15, 1.04

```

--------------------------------

### ls --dired actual example

Source: https://www.gnu.org/software/coreutils/manual/html_node/What-information-is-listed.html

A complete example of `ls -gloRF --dired a` showing the main output and the additional --dired lines with offsets. The pairs of offsets on the //DIRED// line delimit file names: f1, f2, sub, sub2, deeper, file. The //SUBDIRED// line delimit directory names: a, a/sub, a/sub/deeper, a/sub2.

```shell
$ mkdir -p a/sub/deeper a/sub2
$ touch a/f1 a/f2
$ touch a/sub/deeper/file
$ ls -gloRF --dired a
  a:
  total 8
  -rw-r--r-- 1    0 Jun 10 12:27 f1
  -rw-r--r-- 1    0 Jun 10 12:27 f2
  drwxr-xr-x 3 4096 Jun 10 12:27 sub/
  drwxr-xr-x 2 4096 Jun 10 12:27 sub2/

  a/sub:
  total 4
  drwxr-xr-x 2 4096 Jun 10 12:27 deeper/

  a/sub/deeper:
  total 0
  -rw-r--r-- 1 0 Jun 10 12:27 file

  a/sub2:
  total 0
//DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
//SUBDIRED// 2 3 167 172 228 240 290 296
//DIRED-OPTIONS// --quoting-style=literal

```

--------------------------------

### Example output of --resolution

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Example output of the --resolution option when the clock resolution is 1 millisecond. The format defaults to %s.%N.

```text
0.001000000
```

--------------------------------

### Better example: cd .. and ln -s adir/a .

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows a better approach: change to the target directory before creating symlinks to avoid confusion.

```shell
# Change to the target before creating symlinks to avoid being confused.
cd ..
ln -s adir/a .
```

--------------------------------

### touch obsolete syntax examples

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows portable alternatives to the obsolete touch syntax on systems predating POSIX 1003.1-2001. The examples avoid ambiguity by using './' or the -t option.

```shell
touch ./12312359 main.c
```

```shell
touch -t 12312359 main.c
```

--------------------------------

### Create pre-sorted input files file1 and file2

Source: https://www.gnu.org/software/coreutils/manual/html_node/Paired-and-unpaired-lines.html

These two files are used by all examples in this section. They must be sorted before joining.

```shell
$ cat file1
a 1
b 2

```

```shell
$ cat file2
a A
c C

```

--------------------------------

### uptime command example output

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Example output of the 'uptime' command, which prints the current time, system uptime, number of logged-in users, and load average. The output shown is '14:07  up   3:35,  3 users,  load average: 1.39, 1.15, 1.04'.

```shell
$ uptime
 14:07  up   3:35,  3 users,  load average: 1.39, 1.15, 1.04
```

--------------------------------

### numfmt --unit-separator examples

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Examples showing how to use --unit-separator to add a space on output, disable blanks on input, support blanks on input, and output a non-breaking space.

```shell
--unit-separator=' '
```

```shell
--unit-separator=''
```

```shell
--delimiter=''
```

```shell
-d '' --unit-separator=$'\u00A0'
```

--------------------------------

### chown --from example: find and xargs

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

An example from the --from=OLD-OWNER option description. It shows a dangerous approach to changing ownership of all files owned by OLDUSER to NEWUSER, using find and xargs. The interval between find testing the owner and chown running can be large, creating a security risk.

```shell
find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
```

--------------------------------

### chown --from example: find -exec

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

An alternative to the previous example, using find -exec to invoke chown for each file as it is found. This narrows the gap but is very slow if there are many affected files.

```shell
find / -owner OLDUSER -exec chown -h NEWUSER {} \;
```

--------------------------------

### dirname usage examples

Source: https://www.gnu.org/software/coreutils/manual/html_node/dirname-invocation.html

Examples of using dirname. The first command outputs '/usr/bin', the second outputs 'dir1' followed by 'dir2', and the third outputs '.'. The comments indicate the expected output for each command.

```bash
# Output "/usr/bin".
dirname /usr/bin/sort
dirname /usr/bin//.//

# Output "dir1" followed by "dir2"
dirname dir1/str dir2/str

# Output ".".
dirname stdio.h
```

--------------------------------

### chmod examples: recursive umask default

Source: https://www.gnu.org/software/coreutils/manual/html_node/chmod-invocation.html

Example that recursively sets permissions to the umask default, assuming execute permissions for directories and already executable files.

```bash
# Set file permissions of DIR and subsidiary files to
# be the umask default, assuming execute permissions for
# directories and for files already executable.
chmod -R a=,+rwX dir

```

--------------------------------

### Create and enter an empty directory

Source: https://www.gnu.org/software/coreutils/manual/html_node/csplit-invocation.html

Creates an empty directory named 'd' and changes into it, as the first step of the usage example.

```shell
$ mkdir d && cd d

```

--------------------------------

### cp --parents example

Source: https://www.gnu.org/software/coreutils/manual/html_node/cp-invocation.html

Copies a/b/c to existing_dir/a/b/c, creating missing intermediate directories. The last argument must be an existing directory.

```shell
cp --parents a/b/c existing_dir

```

--------------------------------

### env --default-signal example with seq and head

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Runs 'seq' with SIGINT and SIGPIPE set to default, demonstrating that the command terminates normally when piped to head.

```shell
env --default-signal=PIPE,INT seq 1000 | head -n1
```

--------------------------------

### basename examples: strip directory and suffix

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Examples showing how to use 'basename' to strip directory components and optional suffixes. The first command outputs 'sort', the second and third output 'stdio', and the fourth outputs 'stdio' followed by 'stdlib'.

```shell
# Output "sort".
basename /usr/bin/sort
```

```shell
# Output "stdio".
basename include/stdio.h .h
```

```shell
# Output "stdio".
basename -s .h include/stdio.h
```

```shell
# Output "stdio" followed by "stdlib"
basename -a -s .h include/stdio.h include/stdlib.h
```

--------------------------------

### basenc decoding examples

Source: https://www.gnu.org/software/coreutils/manual/html_node/basenc-invocation.html

Commands showing how to decode binary strings using --base2msbf and --base2lsbf with the --decode option, each followed by its output.

```bash
$ printf 01010100 | basenc --base2msbf --decode
T
```

```bash
$ printf 01010100 | basenc --base2lsbf --decode
*
```

--------------------------------

### env --debug example output

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows verbose output of env when using --debug, including unset, setenv, and executing steps.

```shell
$ env -v -uTERM A=B uname -s
unset:    TERM
setenv:   A=B
executing: uname
   arg[0]= 'uname'
   arg[1]= '-s'
Linux
```

--------------------------------

### expr: Examples with operators and outputs

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows several expr invocations and their outputs, including the '\+' operator, capturing groups, index, and error handling. The last example demonstrates that 'index' is a keyword and must be quoted.

```shell
expr aaa : 'a\+'
⇒ 3
```

```shell
expr abc : 'a\(.\)c'
⇒ b
```

```shell
expr index abcdef cz
⇒ 3
```

```shell
expr index index a
error→ expr: syntax error
```

```shell
expr index + index a
⇒ 0
```

--------------------------------

### stat timestamp formatting examples

Source: https://www.gnu.org/software/coreutils/manual/html_node/stat-invocation.html

Shows how to use the `%Y` format with zero padding, space alignment, and precision to control timestamp output. The examples use `stat -c` with different format strings and display the resulting output.

```shell
zero pad:
  $ stat -c '[%015Y]' /usr
  [000001288929712]
space align:
  $ stat -c '[%15Y]' /usr
  [     1288929712]
  $ stat -c '[%-15Y]' /usr
  [1288929712     ]
precision:
  $ stat -c '[%.3Y]' /usr
  [1288929712.114]
  $ stat -c '[%.Y]' /usr
  [1288929712.114951834]
```

--------------------------------

### dd nocache usage examples

Source: https://www.gnu.org/software/coreutils/manual/html_node/dd-invocation.html

These examples demonstrate the 'nocache' flag for dd. The first advises dropping the cache for the whole file, the second ensures it, the third advises dropping for part of the file, and the fourth streams data using the read-ahead cache. The 'sync' conversions are recommended to maximize effectiveness.

```shell
# Advise to drop cache for whole file
dd if=ifile iflag=nocache count=0
```

```shell
# Ensure drop cache for the whole file
dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0
```

```shell
# Advise to drop cache for part of file
# The kernel will consider only complete and
# already persisted pages.
dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null
```

```shell
# Stream data using just the read-ahead cache.
# See also the 'direct' flag.
dd if=ifile of=ofile iflag=nocache oflag=nocache,sync
```

--------------------------------

### Printing the current environment

Source: https://www.gnu.org/software/coreutils/manual/html_node/env-invocation.html

Example output of 'env' piped to 'sort' to display the environment variables in sorted order.

```shell
$ env | LC_ALL=C sort
EDITOR=emacs
LOGNAME=rms
PATH=.:/gnubin:/hacks
```

--------------------------------

### wc --bytes --words example

Source: https://www.gnu.org/software/coreutils/manual/html_node/wc-invocation.html

Shows that options do not undo each other; this command prints both byte counts and word counts.

```shell
wc --bytes --words

```

--------------------------------

### ls --dired example with mkdir and touch

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Demonstrates the --dired output format. The command creates a directory structure and lists it with -gloRF --dired, showing the //DIRED//, //SUBDIRED//, and //DIRED-OPTIONS// lines with byte offsets for file and directory names.

```shell
$ mkdir -p a/sub/deeper a/sub2
$ touch a/f1 a/f2
$ touch a/sub/deeper/file
$ ls -gloRF --dired a
  a:
  total 8
  -rw-r--r-- 1    0 Jun 10 12:27 f1
  -rw-r--r-- 1    0 Jun 10 12:27 f2
  drwxr-xr-x 3 4096 Jun 10 12:27 sub/
  drwxr-xr-x 2 4096 Jun 10 12:27 sub2/

  a/sub:
  total 4
  drwxr-xr-x 2 4096 Jun 10 12:27 deeper/

  a/sub/deeper:
  total 0
  -rw-r--r-- 1 0 Jun 10 12:27 file

  a/sub2:
  total 0
//DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
//SUBDIRED// 2 3 167 172 228 240 290 296
//DIRED-OPTIONS// --quoting-style=literal
```

--------------------------------

### expr examples with index and syntax error

Source: https://www.gnu.org/software/coreutils/manual/html_node/Examples-of-expr.html

Shows several expr examples: extracting a character with a regex, using the index operator, and a syntax error when the argument starts with 'index'. The final example uses '+' to avoid the error.

```shell
expr abc : 'a\(.\)c'
⇒ b
expr index abcdef cz
⇒ 3
expr index index a
error→ expr: syntax error
expr index + index a
⇒ 0

```

--------------------------------

### ls --ignore example with multiple patterns

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows how to use multiple --ignore options to filter out hidden files and backup files. The first pattern ignores names starting with '.' of length 3 or more, the second ignores two-character names starting with '.' except '..', and the third ignores names starting with '#'.

```shell
$ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
```

--------------------------------

### Symbolic mode: o+g

Source: https://www.gnu.org/software/coreutils/manual/html_node/Copying-Permissions.html

Adds the permissions for the file's group to the permissions for other users. For example, starting with mode 664 (rw-rw-r--) results in 666 (rw-rw-rw-), and starting with 741 (rwxr----x) results in 745 (rwxr--r-x).

```plaintext
o+g
```

--------------------------------

### find longest line in .c or .h files using wc -L --files0-from

Source: https://www.gnu.org/software/coreutils/manual/html_node/wc-invocation.html

Example pipeline that finds the length of the longest line in any .c or .h file in the current hierarchy. Uses find with -print0 to produce NUL-terminated names, then wc -L --files0-from=- and tail -n1 to get the maximum.

```shell
find . -name '*.[ch]' -print0 |
  wc -L --files0-from=- | tail -n1

```

--------------------------------

### date padding examples with %d and %m

Source: https://www.gnu.org/software/coreutils/manual/html_node/Padding-and-other-flags.html

Shows default zero padding, no padding with `-`, and space padding with `_` for day and month fields. The output for each command is shown after the `⇒` symbol.

```shell
date +%d/%m -d "Feb 1"
⇒ 01/02
```

```shell
date +%-d/%-m -d "Feb 1"
⇒ 1/2
```

```shell
date +%_d/%_m -d "Feb 1"
⇒  1/ 2
```

--------------------------------

### env --default-signal=PIPE,INT example

Source: https://www.gnu.org/software/coreutils/manual/html_node/env-invocation.html

Runs 'seq' with SIGINT and SIGPIPE set to their default (terminate the program).

```shell
env --default-signal=PIPE,INT seq 1000 | head -n1

```

--------------------------------

### chown with --from option

Source: https://www.gnu.org/software/coreutils/manual/html_node/chown-invocation.html

Example using chown with --from to change ownership only if the file is currently owned by OLDUSER. This narrows the race window but is still not perfect.

```shell
chown -h -R --from=OLDUSER NEWUSER /

```

--------------------------------

### find with exec to change ownership

Source: https://www.gnu.org/software/coreutils/manual/html_node/chown-invocation.html

Example using find with -exec to change ownership of each file individually. This is slow for many files.

```shell
find / -owner OLDUSER -exec chown -h NEWUSER {} \;

```

--------------------------------

### date --rfc-email example output

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Example output of the date command with the --rfc-email option, showing RFC 5322 format.

```shell
Tue, 09 Jul 2020 19:00:37 -0400
```

--------------------------------

### uname -a example output

Source: https://www.gnu.org/software/coreutils/manual/html_node/uname-invocation.html

Example invocation of uname -a and its output. The output may contain internal spaces, so it cannot be parsed reliably.

```text
uname -a
⇒ Linux dumdum.example.org 5.9.16-200.fc33.x86_64 #1 SMP Mon Dec 21 14:08:22 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
```

--------------------------------

### cp -aL with --preserve=links: dereference and hard link example

Source: https://www.gnu.org/software/coreutils/manual/html_node/cp-invocation.html

Similar to the -H example, but uses -L to follow symbolic links during recursive traversal, preserving hard links in the destination. The example creates a directory with a symlink and copies with -aL, showing the resulting hard-linked files.

```shell
$ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
74163295 a
74163295 b

```

--------------------------------

### split -nr/3: round-robin distribution with r/ modifier

Source: https://www.gnu.org/software/coreutils/manual/html_node/split-invocation.html

Uses the r/ modifier to distribute lines in a round-robin fashion across the output files. The output shows lines are assigned cyclically: xaa gets 06 and 09, xab gets 07 and 10, xac gets 08.

```shell
$ seq -w 6 10 > k; split -nr/3 k; head xa?
==> xaa <==
06
09

==> xab <==
07
10

==> xac <==
08

```

--------------------------------

### chroot with env --chdir example

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows how to use 'env --chdir' to change the working directory for a command run via chroot, and how to combine it with environment variables and timeout.

```shell
# Run 'true' with /chroot as its root directory and /srv as its working
# directory.
chroot /chroot env --chdir=/srv true
# Run 'true' with /build as its working directory, FOO=bar in its
# environment, and a time limit of five seconds.
env --chdir=/build FOO=bar timeout 5 true
```

--------------------------------

### comm --total example

Source: https://www.gnu.org/software/coreutils/manual/html_node/comm-invocation.html

Creates two files with sample lines and runs 'comm --total -123' to print a summary of line counts. The output shows the totals for lines unique to file1, unique to file2, and common to both.

```shell
$ printf '%s\n' a b c d e     > file1
$ printf '%s\n'   b c d e f g > file2
$ comm --total -123 file1 file2
1       2       4       total
```

--------------------------------

### printf missing arguments example

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Example command showing that missing ARGUMENTs are treated as null strings or zeros. The command 'printf %sx%d' prints 'x0'.

```shell
printf %sx%d
```

--------------------------------

### arch synopsis

Source: https://www.gnu.org/software/coreutils/manual/html_node/arch-invocation.html

Shows the command-line syntax for arch. The program accepts only the Common options. arch is not installed by default, so portable scripts should not rely on its existence. An exit status of zero indicates success, and a nonzero value indicates failure.

```text
arch [option]

```

--------------------------------

### seq -f format example

Source: https://www.gnu.org/software/coreutils/manual/html_node/seq-invocation.html

Uses the `-f` option to format output with a floating-point conversion specification. The example shows output with parentheses and scientific notation.

```shell
$ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
(-9.00E+05)
( 2.00E+05)
( 1.30E+06)
```

--------------------------------

### id -Gn --zero example

Source: https://www.gnu.org/software/coreutils/manual/html_node/id-invocation.html

Example output of the id command with -Gn --zero options, showing groups delimited by NUL characters.

```bash
$ id -Gn --zero
users <NUL> devs <NUL>

```

--------------------------------

### tee with two process substitutions

Source: https://www.gnu.org/software/coreutils/manual/html_node/tee-invocation.html

Extends the previous example to compute SHA-256 and SHA3-256 checksums in parallel using process substitution. Requires bash, zsh, or ksh.

```bash
wget -O - https://example.com/dvd.iso \
  | tee >(cksum -a sha2 -l 256 > dvd.sha256) \
        >(cksum -a sha3 -l 256 > dvd.sha3) \
  > dvd.iso

```

--------------------------------

### mkdir synopsis

Source: https://www.gnu.org/software/coreutils/manual/html_node/mkdir-invocation.html

Shows the general command-line syntax for mkdir: mkdir [option]... name...

```bash
mkdir [option]... name...

```

--------------------------------

### Example output of --rfc-email

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Example output of the --rfc-email option, which uses the format %a, %d %b %Y %H:%M:%S %z in the C locale so abbreviations are always in English.

```text
Mon, 09 Jul 2020 17:00:00 -0400
```

--------------------------------

### printf FORMAT reuse example

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Example command showing that the FORMAT argument is reused as necessary to convert all given ARGUMENTs. The command 'printf %s a b' outputs 'ab'.

```shell
printf %s a b
```

--------------------------------

### factor timing example with Mersenne primes

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Demonstrates factoring the product of the eighth and ninth Mersenne primes using shell variables and the 'time' command, showing the output and timing.

```shell
$ M8=$(echo 2^31-1 | bc)
$ M9=$(echo 2^61-1 | bc)
$ n=$(echo "$M8 * $M9" | bc)
$ bash -c "time factor $n"
4951760154835678088235319297: 2147483647 2305843009213693951

real	0m0.006s
user	0m0.004s
sys	0m0.002s
```

--------------------------------

### Tweak output with --padding or --format

Source: https://www.gnu.org/software/coreutils/manual/html_node/numfmt-invocation.html

Shows how to pad output to a fixed width using --padding (positive for right-aligned, negative for left-aligned) or --format with a width specifier. The examples use du -s * and demonstrate right-aligned, left-aligned, and format-based padding.

```shell
# Pad to 10 characters, right-aligned
$ du -s * | numfmt --to=si --padding=10
      2.5k config.log
       108 config.status
      1.7k configure
        20 configure.ac

# Pad to 10 characters, left-aligned
$ du -s * | numfmt --to=si --padding=-10
2.5k       config.log
108        config.status
1.7k       configure
20         configure.ac

# Pad to 10 characters, left-aligned, using 'format'
$ du -s * | numfmt --to=si --format="%10f"
      2.5k config.log
       108 config.status
      1.7k configure
        20 configure.ac

# Pad to 10 characters, left-aligned, using 'format'
$ du -s * | numfmt --to=si --padding="%-10f"
2.5k       config.log
108        config.status
1.7k       configure
20         configure.ac
```

--------------------------------

### sum synopsis: sum [option]... [file]...

Source: https://www.gnu.org/software/coreutils/manual/html_node/sum-invocation.html

Shows the command-line syntax for `sum`. Use this to invoke `sum` with optional options and file arguments; if no files are given, or for a file named '-', it reads standard input.

```text
sum [option]... [file]...

```

--------------------------------

### env -S: '#' comment character examples

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows how '#' as the first character of an argument makes 'env' ignore the rest of the string, and how '\#' reverses this behavior. The examples use single quotes on the command line.

```shell
$ env -S'printf %s\n A B C'
A
B
C
```

```shell
$ env -S'printf %s\n A# B C'
A#
B
C
```

```shell
$ env -S'printf %s\n A #B C'
A
```

```shell
$ env -S'printf %s\n A \#B C'
A
#B
C
```

```shell
$ env -S'printf %s\n A\cB C'
A
```

--------------------------------

### nice synopsis

Source: https://www.gnu.org/software/coreutils/manual/html_node/nice-invocation.html

Shows the command-line syntax for 'nice'. If no arguments are given, it prints the current niceness; otherwise it runs the given command with its niceness adjusted (incremented by 10 by default).

```bash
nice [option]... [command [arg]...]

```

--------------------------------

### env -S printf examples demonstrating comments and escapes

Source: https://www.gnu.org/software/coreutils/manual/html_node/env-invocation.html

Command-line examples showing how env -S handles comments (#) and the \c escape sequence. Single quotes are used on the command line. The output for each command is shown.

```shell
$ env -S'printf %s\n A B C'
A
B
C

$ env -S'printf %s\n A# B C'
A#
B
C

$ env -S'printf %s\n A #B C'
A

$ env -S'printf %s\n A \#B C'
A
#B
C

$ env -S'printf %s\n A\cB C'
A
```

--------------------------------

### Command-line equivalent of hello.pl: env -S'perl -T -w' hello.pl

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows how to test 'env -S' on the command line. Single quotes are used to emulate a single parameter, and the command is equivalent to the 'hello.pl' script.

```bash
$ env -S'perl -T -w' hello.pl
```

--------------------------------

### expand synopsis

Source: https://www.gnu.org/software/coreutils/manual/html_node/expand-invocation.html

Shows the command-line syntax for expand: expand [option]... [file]...

```bash
expand [option]... [file]...

```

--------------------------------

### touch -r with relative date example

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Illustrates combining the --reference and --date options to set a timestamp relative to a reference file. The example sets the timestamp to five seconds before the reference file's timestamp.

```shell
-r foo -d '-5 seconds'
```

--------------------------------

### tsort call graph example

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows a realistic example where 'tsort' is used to order functions based on a call graph. The input is a list of function call pairs, and the output is piped through 'tac' to produce a reverse topological order.

```text
main parse_options
main tail_file
main tail_forever
tail_file pretty_name
tail_file write_header
tail_file tail
tail_forever recheck
tail_forever pretty_name
tail_forever write_header
tail_forever dump_remainder
tail tail_lines
tail tail_bytes
tail_lines start_lines
tail_lines dump_remainder
tail_lines file_lines
tail_lines pipe_lines
tail_bytes xlseek
tail_bytes start_bytes
tail_bytes dump_remainder
tail_bytes pipe_bytes
file_lines dump_remainder
recheck pretty_name
```

```shell
example$ tsort call-graph | tac
dump_remainder
start_lines
file_lines
pipe_lines
xlseek
start_bytes
pipe_bytes
tail_lines
tail_bytes
pretty_name
write_header
tail
recheck
parse_options
tail_file
tail_forever
main
```

--------------------------------

### Efficient download and checksum with process substitution

Source: https://www.gnu.org/software/coreutils/manual/html_node/tee-invocation.html

Uses tee with process substitution to compute the checksum while downloading. Requires bash, zsh, or ksh; not /bin/sh. Use -p if process substitutions might exit early.

```bash
# slightly contrived, to demonstrate process substitution
wget -O - https://example.com/dvd.iso \
  | tee >(cksum -a sha2 -l 256 > dvd.sha256) > dvd.iso

```

--------------------------------

### chown examples: change owner, group, and recursive

Source: https://www.gnu.org/software/coreutils/manual/html_node/chown-invocation.html

Three example invocations of chown: changing the owner of /u to root, changing owner and group to root:staff, and recursively changing owner of /u and subfiles to root with -hR.

```shell
# Change the owner of /u to "root".
chown root /u
```

```shell
# Likewise, but also change its group to "staff".
chown root:staff /u
```

```shell
# Change the owner of /u and subfiles to "root".
chown -hR root /u
```

--------------------------------

### tail --pid example: watch build output

Source: https://www.gnu.org/software/coreutils/manual/html_node/tail-invocation.html

Shows how to run make and tail together so tail exits when the build completes. The --pid option makes tail stop after the specified process (the make job) no longer exists.

```shell
$ make >& makerr & tail --pid=$! -f makerr

```

--------------------------------

### Create input file with version-like numbers

Source: https://www.gnu.org/software/coreutils/manual/html_node/Version-sort-is-not-the-same-as-numeric-sort.html

Creates the input4 file used by the numeric and version sort examples. The file contains lines such as 8.10, 8.5, 8.1, 8.01, 8.010, 8.100, and 8.49.

```shell
$ cat input4
8.10
8.5
8.1
8.01
8.010
8.100
8.49
```

--------------------------------

### sync synopsis

Source: https://www.gnu.org/software/coreutils/manual/html_node/sync-invocation.html

Shows the command-line synopsis for sync: sync [option] [file]...

```bash
sync [option] [file]...
```

--------------------------------

### head synopsis: head [OPTION]... [FILE]...

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows the command-line syntax for the head utility. It prints the first 10 lines of each FILE by default, or reads from standard input if no files are given or when FILE is '-'.

```bash
head [OPTION]... [FILE]...
```

--------------------------------

### mv command synopses

Source: https://www.gnu.org/software/coreutils/manual/html_node/mv-invocation.html

The basic usage patterns for the mv command.

```bash
mv [option]... [-T] source dest
mv [option]... source... directory
mv [option]... -t directory source...
```

--------------------------------

### Check acceleration mode with --debug for wc and cksum

Source: https://www.gnu.org/software/coreutils/manual/html_node/Hardware-Acceleration.html

The --debug option reports the current acceleration mode. The wc example shows using avx2 hardware support, while the cksum example shows avx512 and avx2 support not detected and using pclmul hardware support.

```bash
$ wc -l --debug /dev/null >/dev/null
wc: using avx2 hardware support

```

```bash
$ cksum --debug /dev/null >/dev/null
cksum: avx512 support not detected
cksum: avx2 support not detected
cksum: using pclmul hardware support

```

--------------------------------

### ln -s example: relative file names survive directory moves

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Shows how to create symbolic links using relative paths, which remain valid when directories are moved and work across networked file systems.

```shell
# Relative file names survive directory moves and also
# work across networked file systems.
ln -s afile anotherfile
ln -s ../adir/afile yetanotherfile
```

--------------------------------

### cp -aH with --preserve=links: hard link preservation example

Source: https://www.gnu.org/software/coreutils/manual/html_node/cp-invocation.html

Shows that with -aH, cp dereferences command-line arguments and preserves hard links between source files, resulting in hard-linked files in the destination. The example uses mkdir, : >, ln -s, cp -aH, and ls -i1 to demonstrate the behavior.

```shell
$ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
74161745 a
74161745 b

```

--------------------------------

### shuf example with here-document

Source: https://www.gnu.org/software/coreutils/manual/html_node/shuf-invocation.html

Shuffles lines from a here-document. The output is a random permutation of the input lines.

```bash
shuf <<EOF
A man,
a plan,
a canal:
Panama!
EOF

```

--------------------------------

### tee with process substitution to compute SHA-256 checksum

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Uses tee with process substitution to write the downloaded file to disk and compute its SHA-256 checksum in parallel. Requires a shell supporting process substitution (zsh, bash, ksh), not /bin/sh. The -p option may be needed if process substitutions exit early.

```shell
wget -O - https://example.com/dvd.iso \
  | tee >(cksum -a sha2 -l 256 > dvd.sha256) > dvd.iso
```

--------------------------------

### shuf -i example

Source: https://www.gnu.org/software/coreutils/manual/html_node/shuf-invocation.html

Shuffles the range of integers from 1 to 4. The output is a random permutation of those integers.

```bash
shuf -i 1-4

```

--------------------------------

### Word frequency pipeline: Example output

Source: https://www.gnu.org/software/coreutils/manual/coreutils.txt

Sample output from the word frequency pipeline, showing word counts.

```shell
      60 a
       2 able
       6 about
       1 above
       2 accomplish
       1 acquire
       1 actually
       2 additional
```

--------------------------------

### stat --format example for device and inode numbers

Source: https://www.gnu.org/software/coreutils/manual/html_node/stat-invocation.html

Shows how to use `--format` to print device and inode numbers for multiple files. The output is automatically newline-terminated, producing one line per operand.

```bash
$ stat --format=%d:%i / /usr
2050:2
2057:2

```

--------------------------------

### shuf -e example

Source: https://www.gnu.org/software/coreutils/manual/html_node/shuf-invocation.html

Shuffles command-line arguments as input lines. The output is a random permutation of the given arguments.

```bash
shuf -e clubs hearts diamonds spades

```

--------------------------------

### env --ignore-signal=INT example

Source: https://www.gnu.org/software/coreutils/manual/html_node/env-invocation.html

Runs 'seq' with SIGINT set to be ignored – pressing Ctrl-C will not terminate it.

```shell
env --ignore-signal=INT seq inf > /dev/null

```
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