Master Shell Logical Operators to Supercharge Your Bash Scripts

1. Logical Operators

File and directory test flags -f – check if a file exists -d – check if a directory exists -b – check for a block device -c – check for a character device -S – check for a socket -L – check for a symbolic link -e – check if something exists

Program‑related flags -G – true if the file’s group ID matches the effective GID -O – true if the file’s owner ID matches the effective UID -p – true if the file is a named pipe (FIFO)

File attribute flags -r – readable -w – writable -x – executable -s – non‑empty -u – set‑UID bit set -g – set‑GID bit set -k – sticky bit set

File comparison operators -nt – first file is newer than the second -ot – first file is older than the second -ef – both names refer to the same file

Logical AND / OR && – logical AND || – logical OR

2. Comparison Symbols

=

– equal (string comparison inside []) != – not equal (string comparison inside []) < – less than (integer comparison; inside [] it must be a string) > – greater than (integer comparison; same restriction) -eq – equal (integer) -ne – not equal (integer) -lt – less than (integer) -gt – greater than (integer) -le – less than or equal (integer) -ge – greater than or equal (integer) -a – logical AND (old syntax) -o – logical OR (old syntax) -z – string is empty -n – string is non‑empty

3. Conditional Expressions

test command

Usage: test EXPRESSION Examples:

[root@localhost ~]# test 1 = 1 && echo 'ok'
ok
[root@localhost ~]# test -d /etc/ && echo 'ok'
ok
[root@localhost ~]# test 1 -eq 1 && echo 'ok'
ok
[root@localhost ~]# if test 1 = 1 ; then echo 'ok'; fi
ok

Note: All operators and operands must be separated by spaces.

Bracket expressions

Single brackets []:

[root@localhost ~]# [ 1 -eq 1 ] && echo 'ok'
ok
[root@localhost ~]# [ 2 < 1 ] && echo 'ok'
-bash: 2: No such file or directory
[root@localhost ~]# [ 2 -gt 1 -a 3 -lt 4 ] && echo 'ok'
ok

Double brackets [[]] support < and > without escaping and allow logical operators || and &&:

[root@localhost ~]$ [[ 2 < 3 ]] && echo 'ok'
ok
[root@localhost ~]$ [[ 2 < 3 && 4 > 5 ]] && echo 'ok'
ok

Performance comparison (100 000 iterations):

time (for m in {1..100000}; do test -d .; done)
real 0m0.658s
user 0m0.558s
sys 0m0.100s

time (for m in {1..100000}; do [ -d . ]; done)
real 0m0.609s
user 0m0.524s
sys 0m0.085s

time (for m in {1..100000}; do [[ -d . ]]; done)
real 0m0.311s
user 0m0.275s
sys 0m0.036s

When compatibility with older Bash or POSIX sh is not required, [[]] offers stronger compatibility and better performance for conditional checks.