Dart
Dart
HTML Canvas
HTML Canvas
Redis
Redis
Bash
Bash
JavaScript
JavaScript
Bash
Bash

Bash Conditionals

logical and, or

if [ "$1" = 'y' -a $2 -gt 0 ]; then
    echo "yes"
fi
if [ "$1" = 'n' -o $2 -lt 0 ]; then
    echo "no"
fi

More conditions

Condition Description
[[ -o noclobber ]] If OPTION is enabled
[[ ! EXPR ]] Not
[[ X && Y ]] And
[[ X || Y ]] Or

File conditions

Condition Description
[[ -e FILE ]] Exists
[[ -d FILE ]] Directory
[[ -f FILE ]] File
[[ -h FILE ]] Symlink
[[ -s FILE ]] Size is > 0 bytes
[[ -r FILE ]] Readable
[[ -w FILE ]] Writable
[[ -x FILE ]] Executable
[[ f1 -nt f2 ]] f1 newer than f2
[[ f1 -ot f2 ]] f2 older than f1
[[ f1 -ef f2 ]] Same files

Example

#String

if [[ -z "$string" ]]; then
    echo "String is empty"
elif [[ -n "$string" ]]; then
    echo "String is not empty"
else
    echo "This never happens"
fi

#Combinations

if [[ X && Y ]]; then
    ...
fi

#Equal

if [[ "$A" == "$B" ]]; then
    ...
fi

#Regex

if [[ '1. abc' =~ ([a-z]+) ]]; then
    echo ${BASH\_REMATCH[1]}
fi

#Smaller

if (( $a < $b )); then
   echo "$a is smaller than $b"
fi

#Exists

if [[ -e "file.txt" ]]; then
    echo "file exists"
fi

String conditions

Condition Description
[[ -z STR ]] Empty string
[[ -n STR ]] Not empty string
[[ STR == STR ]] Equal
[[ STR = STR ]] Equal (Same above)
[[ STR < STR ]] Less than (ASCII)
[[ STR > STR ]] Greater than (ASCII)
[[ STR != STR ]] Not Equal
[[ STR =~ STR ]] Regexp

Integer conditions

Condition Description
[[ 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
(( NUM < NUM )) Less than
(( NUM <= NUM )) Less than or equal
(( NUM > NUM )) Greater than
(( NUM >= NUM )) Greater than or equal
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