Bash if expressions cheatsheet.

README.md

Bash if expressions cheatsheet

• Table
  • String
  • Integer
  • File system
  • File compare modification/exists
  • Combine expressions
• Notes
• Reference

Boolean
Is true *	VAR=: if [[ $VAR ]]
Is false	VAR= if [[ ! $VAR ]]
String
Is equal	if [[ $VAR1 == $VAR2 ]]
Not equal	if [[ $VAR1 != $VAR2 ]]
Is empty / zero length	if [[ -z $VAR ]]
Not empty / non-zero length	if [[ -n $VAR ]]
Less than (ASCII alpha)	if [[ $VAR1 < $VAR2 ]]
Greater than (ASCII alpha)	if [[ $VAR1 > $VAR2 ]]
Regular expression **	if [[ $VAR =~ ^my.+regexp$ ]]
Regular expression not **	if [[ ! $VAR =~ ^my.+regexp$ ]]
String contains ***	if [[ $VAR =~ "needle" ]]
Integer
Is equal	if [[ $VAR1 -eq $VAR2 ]]
Not equal	if [[ $VAR1 -ne $VAR2 ]]
Less than	if [[ $VAR1 -lt $VAR2 ]]
Less than or equal	if [[ $VAR1 -le $VAR2 ]]
Greater than	if [[ $VAR1 -gt $VAR2 ]]
Greater than or equal	if [[ $VAR1 -ge $VAR2 ]]
File system
Is file (file, dir, symlink, anything)	if [[ -e $FILE_PATH ]]
Is regular file	if [[ -f $FILE_PATH ]]
Is regular file, is readable	if [[ -r $FILE_PATH ]]
Is regular file, is writable	if [[ -w $FILE_PATH ]]
Is regular file, is executable	if [[ -x $FILE_PATH ]]
Is regular file, not zero size	if [[ -s $FILE_PATH ]]
Is directory	if [[ -d $FILE_PATH ]]
Is symlink	if [[ -h $FILE_PATH ]]
Is socket	if [[ -S $FILE_PATH ]]
File compare modification/exists
Is FILE1 newer than FILE2 ...or FILE1 exists and FILE2 does not	if [[ $FILE1 -nt $FILE2 ]]
Is FILE1 older than FILE2 ...or FILE2 exists and FILE1 does not	if [[ $FILE1 -ot $FILE2 ]]
Combine expressions
If EXPR1 and EXPR2 are true	if [[ (EXPR1) && (EXPR2) ]]
If EXPR1 and EXPR2 are true	if [ (EXPR1) -a (EXPR2) ]
If EXPR1 or EXPR2 are true	if [[ (EXPR1) || (EXPR2) ]]
If EXPR1 or EXPR2 are true	if [ (EXPR1) -o (EXPR2) ]

Notes

• *: Use of : here as a NOP operation, which will always return true.
• **: Regular expression captures available via array ${BASH_REMATCH[*]}, ${BASH_REMATCH[1]}, etc.
• ***: This behavior for the =~ operator was introduced between Bash 3.1 -> 3.2.

Reference

• Most lifted from here: https://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html
• Difference between [ ] and [[ ]]: https://mywiki.wooledge.org/BashFAQ/031
• Bash NOP (no op) :: https://en.wikipedia.org/wiki/NOP#Shell_Scripting_.28bash.2C_zsh.2C_etc.29
• GNU Bash reference manual: https://www.gnu.org/software/bash/manual/bashref.html