Operator¶

AND and OR¶

No short circuits but &&and || have short circuits

-a: [ -r "$FN" -a ( -f "$FN" -o -p "$FN" ) ]
-o: [ -z "$V1" -o -z "${V2:=YIKES}" ]

Comparison operators¶

https://tldp.org/LDP/abs/html/comparison-ops.html

Always put the $var in quotes

-n is not null
-z is null - has zero length Using -n without quoting, will return true even it's empty
== string comparison
-eq numerical comparison

If always use the math-style symbols for comparison:

do numerical tests with the double-parentheses syntax
do string comparisons with the double-square-brackets syntax

Arithmetic operators¶

=, +=, -=, *=, /=, &=, \=, ^=, <<=, >>= Integer arithmetic:

let 'i += j' 'j *= i'
let n+='i**2 + 1'
n=$(( n + i**2 + 1 ))

File testing unary operators¶

Exists

-d File is a directory
-f File is a regular file
-e File exists
-s File has a size greater than zero

Read/write etc

-r File is readable
-w File is writable
-x File is executable
-N File has been modified since it was last read

Types

-b File is a block special device (for files like /dev/hda1)
-c File is character special (for files like /dev/tty)
-S File is a socket
-p File is a named pipe
-h File is a symbolic link (same as -L )
-L File is a symbolic link (same as -h )

bit set

-k File has its sticky bit set
-u File has its set-user-ID (setuid) bit set
-g File has its set-group-ID (setgid) bit set
-O File is owned by the effective user ID
-G File is owned by the effective group ID

File testing binary operators¶

[ file_1 -nt file_2 ] #file_1 is newer than file_2
[ file_1 -ot file_2 ] #file_1 is older than file_2
[ file_1 -ef file_2 ] #file_1 and file_2 have the same device or inode numbers