Reference · 35 entries

Bash and Linux Commands Reference

A Bash cheat sheet: builtins, conditions, loops, functions, arrays, expansions, redirection, strict mode, and the Linux text tools grep, sed, awk, sort, find and more, with real examples.

Bash 5 Version history

Every example is a Bash script that was run on Linux (Bash 5, GNU coreutils) when this page was built, so the output is real. For step-by-step explanations, see the Bash tutorial and the Linux and Bash for Developers course.

Shell Builtins and Syntax

Bash builtins and syntax: printf, read, conditions, loops, functions, arrays, expansions, redirection, strict mode and traps.

Name	Description
`printf`	Print formatted text with format specifiers like %s, %d and %.2f; more portable and predictable than echo.
`read`	Read a line from standard input into variables, splitting on IFS; use -r to keep backslashes and -p for a prompt.
`mapfile`	Read all lines of input into an indexed array at once (also called readarray), optionally trimming newlines with -t.
`[[ ]]`	Bash's conditional expression: compare strings and numbers, test files, and match glob patterns or regular expressions.
`if`	Run commands depending on whether a command succeeds (exit status 0), with optional elif and else branches.
`case`	Match a value against glob patterns and run the first matching branch; cleaner than long if/elif chains.
`for`	Loop over words, files, ranges or array elements, or use the C-style form for counters.
`while`	Repeat commands while a condition succeeds; with read, it's the standard way to process input line by line.
`function`	Group commands into a named function that takes arguments like a script ($1, $@) and returns an exit status.
`local`	Declare variables that exist only inside the current function, so they don't overwrite globals with the same name.
`declare`	Declare variables with attributes: arrays, associative arrays, integers, read-only values and exported variables.
`arrays`	Indexed and associative arrays: create, append, read elements, count, slice and loop over them safely.
`${...} expansion`	Defaults, length, substrings, prefix and suffix removal, search and replace, and case conversion on variables.
`$(( )) arithmetic`	Evaluate integer arithmetic and comparisons with $(( )) and (( )); Bash has no floating point, so use awk or bc.
`redirection`	Send output to files, read input from files, merge stderr into stdout, and discard output with /dev/null.
`here-document`	Feed multiple lines to a command with <<EOF; quote the marker to stop variable expansion, use <<- to strip tabs.
`set -euo pipefail`	Turn on strict mode: exit on errors (-e), fail on unset variables (-u), and fail pipelines when any part fails.
`trap`	Run commands when the script exits or receives a signal; the standard way to clean up temporary files and child processes.
`export`	Mark variables so child processes inherit them; one-off variables can also be set for a single command.
`source`	Run a file's commands in the current shell, so its variables and functions stay defined; . is the POSIX spelling.
`getopts`	Parse short command-line options such as -v and -o FILE in scripts, with errors for unknown options.

Text and System Tools

Linux tools used with Bash: grep, sed, awk, cut, sort, uniq, tr, find, xargs, head, tail, wc, chmod, tar, ps and kill.

Name	Description
`grep`	Search files or input for lines matching a pattern, with options for case, counts, context, recursion and regex.
`sed`	Edit text streams: substitute with s/old/new/, delete or print lines by number or pattern, and edit files in place.
`awk`	Process text by fields: print and filter columns, compute sums and group totals, with a small built-in language.
`cut`	Extract columns from each line by delimiter and field number, or by character positions.
`sort`	Sort lines alphabetically, numerically, in reverse, by a key column, or with human-readable sizes; -u removes duplicates.
`uniq`	Remove or count adjacent duplicate lines; sort first, then use -c to count occurrences or -d to show only duplicates.
`tr`	Translate, squeeze or delete characters, such as changing case, removing carriage returns or splitting words onto lines.
`find`	Find files and directories by name, type, size, age or permissions, and act on them with -exec, -delete or xargs.
`xargs`	Build and run commands from input lines, in batches or in parallel; pair with find -print0 and xargs -0 for safe file names.
`head and tail`	Show the first or last lines of files, skip headers, and follow growing log files with tail -f.
`wc`	Count lines, words, characters and bytes in files or input; wc -l is the usual way to count lines or results.
`chmod`	Change file permissions with symbolic modes (u+x, go-w) or octal numbers (755, 644, 600), optionally recursively.
`tar`	Create, list and extract archives, usually gzip-compressed .tar.gz files, preserving directory structure and permissions.
`ps and kill`	List processes with ps and send signals with kill: SIGTERM to ask a process to stop, SIGKILL only as a last resort.