The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed.
| -a file | True if file exists |
|---|---|
| -b file | True if file exists and is a block special file |
| -c file | True if file exists and is a character special file |
| -d file | True if file exists and is a directory |
| -e file | True if file exists |
| -f file | True if file exists and is a regular file |
| -g file | True if file exists and is set-group-id |
| -h file | True if file exists and is a symbolic link |
| -k file | True if file exists and its ``sticky'' bit is set |
| -n string | True if the length of string is non-zero |
| -p file | True if file exists and is a named pipe (FIFO) |
| -r file | True if file exists and is readable |
| -s file | True if file exists and has a size greater than zero |
| -t fd | True if file descriptor fd is open and refers to a terminal |
| -u file | True if file exists and its set-user-id bit is set |
| -w file | True if file exists and is writable |
| -x file | True if file exists and is executable |
| -z string | True if the length of string is zero |
| -G file | True if file exists and is owned by the effective group id |
| -L file | True if file exists and is a symbolic link |
| -N file | True if file exists and has been modified since it was last read |
| -O file | True if file exists and is owned by the effective user id |
| -S file | True if file exists and is a socket |
| file1 -nt file2 | True if file1 is newer (according to modification date) than file2 |
| file1 -ot file2 | True if file1 is older than file2 |
| file1 -ef file2 | True if file1 and file2 have the same device and inode numbers |
| -o optname | True if shell option optname is enabled |
| string1 == string2 | True if the strings are equal. = may be used in place of == |
| string1 != string2 | True if the strings are not equal |
| string1 < string2 | True if string1 sorts before string2 lexicographically in the current locale |
| string1 > string2 | True if string1 sorts after string2 lexicographically in the current locale |
| arg1 OP arg2 | OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic binary operators return true if arg1 is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal to arg2, respectively. Arg1 and arg2 may be positive or negative integers. |
Ref: Bash 3.2 manpages dated 2006 September 28
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