bash

Redirection

stderr and stdout to a file

$ command > file 2>&1

Test operators

String

op desc example
= is equal to if [ "$a" = "$b" ]
== is equal to if [ "$a" == "$b" ]
!= is not equal to if [ "$a" != "$b" ]
< is less than, in ASCII alphabetical order if [[ "$a" < "$b" ]]; if [ "$a" \< "$b" ]
> is greater than, in ASCII alphabetical order if [[ "$a" > "$b" ]]; if [ "$a" \> "$b" ]
-z string is null, that is, has zero length if [ -z "$a" ]

Integer

op desc example
-eq is equal to if [ "$a" -eq "$b" ]
-ne is not equal to if [ "$a" -ne "$b" ]
-gt is greater than if [ "$a" -gt "$b" ]
-ge is greater than or equal to if [ "$a" -ge "$b" ]
-lt is less than if [ "$a" -lt "$b" ]
-le is less than or equal to if [ "$a" -le "$b" ]
< is less than (("$a" < "$b"))
<= is less than or equal to (("$a" <= "$b"))
> is greater than (("$a" > "$b"))
>= is greater than or equal to (("$a" >= "$b"))

File

op desc example
-h file is a symbolic link if [ -h "$f" ]
-L file is a symbolic link if [ -L "$f" ]
-S file is a socket if [ -S "$f" ]
-t file (descriptor) is associated with a terminal device if [ -t "$f" ]
-r file has read permission (for the user running the test) if [ -r "$f" ]
-w file has write permission (for the user running the test) if [ -w "$f" ]
-x file has execute permission (for the user running the test) if [ -x "$f" ]
-g set-group-id (sgid) flag set on file or directory if [ -g "$f" ]
-u set-user-id (suid) flag set on file if [ -u "$f" ]
-k sticky bit set if [ -k "$f" ]
-O you are owner of file if [ -O "$f" ]
-G group-id of file same as yours if [ -G "$f" ]
-N file modified since it was last read if [ -N "$f" ]
f1 -nt f2 file f1 is newer than f2 if [ f1 -nt f2 "$f" ]
f1 -ot f2 file f1 is older than f2 if [ f1 -ot f2 "$f" ]
f1 -ef f2 files f1 and f2 are hard links to the same file if [ f1 -ef f2 "$f" ]
! “not” – reverses the sense of the tests above (returns true if condition absent). if [ ! "$f" ]