file exists
file exists
This is identical in effect to -e. It has been “deprecated,” [34] and its use is discouraged.
file is a regular
file (not a directory or device
file)
file is not zero size
file is a directory
file is a block device
file is a character device
device0="/dev/sda2" # / (root directory) if [ -b "$device0" ] then echo "$device0 is a block device." fi # /dev/sda2 is a block device. device1="/dev/ttyS1" # PCMCIA modem card. if [ -c "$device1" ] then echo "$device1 is a character device." fi # /dev/ttyS1 is a character device.
file is a pipe
function show_input_type()
{
[ -p /dev/fd/0 ] && echo PIPE || echo STDIN
}
show_input_type "Input" # STDIN
echo "Input" | show_input_type # PIPE
# This example courtesy of Carl Anderson.file is a symbolic link
file is a symbolic link
file is a socket
file (descriptor) is associated with a terminal device
This test option may be used
to check whether the stdin
[ -t 0 ] or
stdout [ -t 1 ]
in a given script is a terminal.
file has read permission (for the user running the test)
file has write permission (for the user running the test)
file has execute permission (for the user running the test)
set-group-id (sgid) flag set on file or directory
If a directory has the sgid
flag set, then a file created within that directory belongs
to the group that owns the directory, not necessarily to
the group of the user who created the file. This may be
useful for a directory shared by a workgroup.
set-user-id (suid) flag set on file
A binary owned by root
with set-user-id flag set
runs with root privileges, even
when an ordinary user invokes it.
[35]
This is useful for executables (such as
pppd and cdrecord)
that need to access system hardware. Lacking the
suid flag, these binaries could not
be invoked by a non-root user.
-rwsr-xr-t 1 root 178236 Oct 2 2000 /usr/sbin/pppd
A file with the suid
flag set shows an s in its
permissions.
sticky bit set
Commonly known as the sticky bit, the save-text-mode flag is a special type of file permission. If a file has this flag set, that file will be kept in cache memory, for quicker access. [36] If set on a directory, it restricts write permission. Setting the sticky bit adds a t to the permissions on the file or directory listing. This restricts altering or deleting specific files in that directory to the owner of those files.
drwxrwxrwt 7 root 1024 May 19 21:26 tmp/
If a user does not own a directory that has the sticky
bit set, but has write permission in that directory, she
can only delete those files that she owns in it. This
keeps users from inadvertently overwriting or deleting
each other's files in a publicly accessible directory,
such as /tmp.
(The owner of the directory or
root can, of course, delete or
rename files there.)
you are owner of file
group-id of file same as yours
file modified since it was last read
file f1 is newer than
f2
file f1 is older than
f2
files f1 and
f2 are hard links to the same
file
“not” -- reverses the sense of the tests above (returns true if condition absent).
Example 7.4. Testing for broken links
#!/bin/bash
# broken-link.sh
# Written by Lee bigelow <ligelowbee@yahoo.com>
# Used in ABS Guide with permission.
# A pure shell script to find dead symlinks and output them quoted
#+ so they can be fed to xargs and dealt with :)
#+ eg. sh broken-link.sh /somedir /someotherdir|xargs rm
#
# This, however, is a better method:
#
# find "somedir" -type l -print0|\
# xargs -r0 file|\
# grep "broken symbolic"|
# sed -e 's/^\|: *broken symbolic.*$/"/g'
#
#+ but that wouldn't be pure Bash, now would it.
# Caution: beware the /proc file system and any circular links!
################################################################
# If no args are passed to the script set directories-to-search
#+ to current directory. Otherwise set the directories-to-search
#+ to the args passed.
######################
[ $# -eq 0 ] && directorys=`pwd` || directorys=$@
# Setup the function linkchk to check the directory it is passed
#+ for files that are links and don't exist, then print them quoted.
# If one of the elements in the directory is a subdirectory then
#+ send that subdirectory to the linkcheck function.
##########
linkchk () {
for element in $1/*; do
[ -h "$element" -a ! -e "$element" ] && echo \"$element\"
[ -d "$element" ] && linkchk $element
# Of course, '-h' tests for symbolic link, '-d' for directory.
done
}
# Send each arg that was passed to the script to the linkchk() function
#+ if it is a valid directoy. If not, then print the error message
#+ and usage info.
##################
for directory in $directorys; do
if [ -d $directory ]
then linkchk $directory
else
echo "$directory is not a directory"
echo "Usage: $0 dir1 dir2 ..."
fi
done
exit $?
Example 31.1, “Hiding the cookie jar”, Example 11.8, “A grep replacement for binary files”, Example 11.3, “Fileinfo: operating on a file list contained in a variable”, Example 31.3, “Creating a ramdisk”, and Example A.1, “mailformat: Formatting an e-mail message” also illustrate uses of the file test operators.
[34] Per the 1913 edition of Webster's Dictionary:
Deprecate ... To pray against, as an evil; to seek to avert by prayer; to desire the removal of; to seek deliverance from; to express deep regret for; to disapprove of strongly.
[35] Be aware that suid binaries may open security holes. The suid flag has no effect on shell scripts.
[36] On Linux systems, the sticky bit is no longer used for files, only on directories.