Look no further than these excellent cheat sheets by data practitioners Dr. Tim Essam and Dr. These compact yet well-organized sheets cover everything you need, from syntax and data processing to plotting and programming, making them handy references to download for quick use.
Getting started
Introduction
This is a quick reference to getting started with Bash scripting.
- Learn bash in y minutes(learnxinyminutes.com)
- Bash Guide(mywiki.wooledge.org)
Example
Variables
String quotes
Shell execution
See Command substitution
Conditional execution
Functions
See: Functions
Conditionals
See: Conditionals
Strict mode
See: Unofficial bash strict mode
Brace expansion
| Expression | Description |
|---|---|
{A,B} | Same as A B |
{A,B}.js | Same as A.js B.js |
{1..5} | Same as 1 2 3 4 5 |
See: Brace expansion
Parameter expansions
Basics
See: Parameter expansion
Substitution
| Code | Description |
|---|---|
${FOO%suffix} | Remove suffix |
${FOO#prefix} | Remove prefix |
${FOO%%suffix} | Remove long suffix |
${FOO##prefix} | Remove long prefix |
${FOO/from/to} | Replace first match |
${FOO//from/to} | Replace all |
${FOO/%from/to} | Replace suffix |
${FOO/#from/to} | Replace prefix |
Substrings
| Expression | Description |
|---|---|
${FOO:0:3} | Substring (position, length) |
${FOO:(-3):3} | Substring from the right |
Length
| Expression | Description |
|---|---|
${#FOO} | Length of $FOO |
Manipulation
Default values
| Expression | Description |
|---|---|
${FOO:-val} | $FOO, or val if unset (or null) |
${FOO:=val} | Set $FOO to val if unset (or null) |
${FOO:+val} | val if $FOO is set (and not null) |
${FOO:?message} | Show error message and exit if $FOO is unset (or null) |
Omitting the : removes the (non)nullity checks, e.g. ${FOO-val} expands to val if unset otherwise $FOO.
Loops
Basic for loop
C-like for loop
Ranges
With step size
Reading lines
Forever
Functions
Defining functions
Returning values
Raising errors
Arguments
| Expression | Description |
|---|---|
$# | Number of arguments |
$* | All arguments |
$@ | All arguments, starting from first |
$1 | First argument |
$_ | Last argument of the previous command |
See Special parameters.
Conditionals
Conditions
Note that [[ is actually a command/program that returns either 0 (true) or 1 (false). Any program that obeys the same logic (like all base utils, such as grep(1) or ping(1)) can be used as condition, see examples.
| Condition | Description |
|---|---|
[[ -z STRING ]] | Empty string |
[[ -n STRING ]] | Not empty string |
[[ STRING STRING ]] | Equal |
[[ STRING != STRING ]] | Not Equal |
[[ NUM -eq NUM ]] | Equal |
[[ NUM -ne NUM ]] | Not equal |
[[ NUM -lt NUM ]] | Less than |
[[ NUM -le NUM ]] | Less than or equal |
[[ NUM -gt NUM ]] | Greater than |
[[ NUM -ge NUM ]] | Greater than or equal |
[[ STRING =~ STRING ]] | Regexp |
(( NUM < NUM )) | Numeric conditions |
More conditions
| Condition | Description |
|---|---|
[[ -o noclobber ]] | If OPTIONNAME is enabled |
[[ ! EXPR ]] | Not |
[[ X && Y ]] | And |
[[ X || Y ]] | Or |
Dos Commands Cheat Sheet
File conditions
| Condition | Description |
|---|---|
[[ -e FILE ]] | Exists |
[[ -r FILE ]] | Readable |
[[ -h FILE ]] | Symlink |
[[ -d FILE ]] | Directory |
[[ -w FILE ]] | Writable |
[[ -s FILE ]] | Size is > 0 bytes |
[[ -f FILE ]] | File |
[[ -x FILE ]] | Executable |
[[ FILE1 -nt FILE2 ]] | 1 is more recent than 2 |
[[ FILE1 -ot FILE2 ]] | 2 is more recent than 1 |
[[ FILE1 -ef FILE2 ]] | Same files |
Example
Arrays
Defining arrays
Working with arrays
Operations
Iteration
Dictionaries
Defining
Declares sound as a Dictionary object (aka associative array).
Working with dictionaries
Iteration
Iterate over values
Iterate over keys
Options
Options
Glob options
Set GLOBIGNORE as a colon-separated list of patterns to be removed from globmatches.
History
Commands
| Command | Description |
|---|---|
history | Show history |
shopt -s histverify | Don’t execute expanded result immediately |
Expansions
| Expression | Description |
|---|---|
!$ | Expand last parameter of most recent command |
!* | Expand all parameters of most recent command |
!-n | Expand nth most recent command |
!n | Expand nth command in history |
!<command> | Expand most recent invocation of command <command> |
Operations
| Code | Description |
|---|---|
!! | Execute last command again |
!!:s/<FROM>/<TO>/ | Replace first occurrence of <FROM> to <TO> in most recent command |
!!:gs/<FROM>/<TO>/ | Replace all occurrences of <FROM> to <TO> in most recent command |
!$:t | Expand only basename from last parameter of most recent command |
!$:h | Expand only directory from last parameter of most recent command |
!! and !$ can be replaced with any valid expansion.
Slices
| Code | Description |
|---|---|
!!:n | Expand only nth token from most recent command (command is 0; first argument is 1) |
!^ | Expand first argument from most recent command |
!$ | Expand last token from most recent command |
!!:n-m | Expand range of tokens from most recent command |
!!:n-$ | Expand nth token to last from most recent command |
!! can be replaced with any valid expansion i.e. !cat, !-2, !42, etc.
Miscellaneous
Numeric calculations
Subshells
Redirection
Inspecting commands
Trap errors
or
Case/switch
Source relative
printf
Batch Commands Cheat Sheet
Directory of script
Getting options
Heredoc
Reading input
Special variables
| Expression | Description |
|---|---|
$? | Exit status of last task |
$! | PID of last background task |
$$ | PID of shell |
$0 | Filename of the shell script |
See Special parameters.
Go to previous directory
Check for command’s result
Grep check
Also see
- Bash-hackers wiki(bash-hackers.org)
- Shell vars(bash-hackers.org)
- Learn bash in y minutes(learnxinyminutes.com)
- Bash Guide(mywiki.wooledge.org)
- ShellCheck(shellcheck.net)