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2

when to use -f or -a tag in if loop

rated 0 times [ 2] [ 0] / answers: 1 / hits: 547 / 1 Year ago, thu, november 24, 2022, 7:40:05

I'm confused between two tages that can be used in if statement in bash scripting.

One is -f and other is -a.

Their description states as follows:

[ -f FILE ] True if FILE exists and is a regular file.

[ -a FILE ] True if FILE exists.

Now, while using the if condition in my shell script how can I know which tag should I use. Like I have a script which takes regular backups using tar and creates a file file-name.tar.gz so how can I know which is a regular file. Thanks.

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ainubt

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1 Year ago

answered 1 Year ago inglehare · Accepted Answer

Regular files are all the text or data file, it can be a binary file as well. For regular files the output of ls -l would be like,

-rw-rw-r-- 1 username group 74 Nov 27 16:03 mytext.txt

In general the first place for a regular file a - should appear. In such cases if [ -f FILE ] would be appropriate.

Non-Regular files are devices, pipes, sockets, tty etc. all other that fall under "Everything is a file" philosophy as pointed out by drc. You can go through Unix_file_types for more information.

You can verify the ls -l output of some like,

crw-rw---- 1 root tty 4, 1 Dec  9 13:41 /dev/tty1

brw-rw---- 1 root disk 1, 11 Dec  9 13:41 /dev/ram11

For all the non-regular files you should use if [ -a FILE ]