Does any one have a template shell script for doing something with ls
for a list of directory names and looping through each one and doing something?
I'm planning to do ls -1d */
to get the list of directory names.
7 Answers
Edited not to use ls where a glob would do, as @shawn-j-goff and others suggested.
Loops plays an important role in bash scripting. After For Loop another loop comes in to picture is Bash while loop. Basically Bash while loop executes sets of command till any condition is satisfied. Once condition turns false execution flow gets out of the bash while loop.
Just use a for..do..done
loop:
You can replace the *
with *.txt
or any other glob that returns a list (of files, directories, or anything for that matter), a command that generates a list, e.g., $(cat filelist.txt)
, or actually replace it with a list.
Within the do
loop, you just refer to the loop variable with the dollar sign prefix (so $f
in the above example). You can echo
it or do anything else to it you want.
For example, to rename all the .xml
files in the current directory to .txt
:
Or even better, if you are using Bash you can use Bash parameter expansions rather than spawning a subshell:
Michael FrankUsing the output of ls
to get filenames is a bad idea. It can lead to malfunctioning and even dangerous scripts. This is because a filename can contain any character except /
and the null
character, and ls
does not use either of those characters as delimiters, so if a filename has a space or a newline, you will get unexpected results.
There are two very good ways of iterating over files. Here, I've used simply echo
to demonstrate doing something with the filename; you can use anything, though.
The first is to use the shell's native globbing features.
The shell expands */
into separate arguments that the for
loop reads; even if there is a space, newline, or any other strange character in the filename, for
will see each complete name as an atomic unit; it's not parsing the list in any way.
If you want to go recursively into subdirectories, then this won't do unless your shell has some extended globbing features (such as bash
's globstar
. If your shell doesn't have these features, or if you want to ensure that your script will work on a variety of systems, then the next option is to use find
.
Here, the find
command will call echo
and pass it an argument of the filename. It does this once for each file it finds. As with the previous example, there is no parsing of a list of filenames; instead, a fileneame is sent completely as an argument.
The syntax of the -exec
argument looks a little funny. find
takes the first argument after -exec
and treats that as the program to run, and every subsequent argument, it takes as an argument to pass to that program. There are two special arguments that -exec
needs to see. The first one is {}
; this argument gets replaced with a filename that the previous parts of find
generates. The second one is ;
, which lets find
know this is the end of the list of arguments to pass to the program; find
needs this because you can continue with more arguments that are intended for find
and not intended for the exec'd program. The reason for the is that the shell also treats
;
specially - it represents the end of a command, so we need to escape it so that the shell gives it as an argument to find
rather than consuming it for itself; another way of getting the shell to not treat it specially is to put it in in quotes: ';'
works just as well as ;
for this purpose.
For files with spaces in you will have to make sure to quote the variable like:
or, you can change the input field separator (IFS) environment variable:
Finally, depending on what you're doing, you may not even need the ls:
If you have GNU Parallel http://www.gnu.org/software/parallel/ installed you can do this:
To rename all .txt to .xml:
Watch the intro video for GNU Parallel to learn more:http://www.youtube.com/watch?v=OpaiGYxkSuQ
whitequarkJust to add to CoverosGene's answer, here is a way to list just the directory names:
Why not set IFS to a newline, then capture the output of ls
in an array? Setting IFS to newline should resolve issues with funny characters in file names; using ls
can be nice because it has a built-in sort facility.
(In testing I was having trouble setting IFS to n
but setting it to newline backspace works, as suggested elsewhere here):
E.g. (assuming desired ls
search pattern passed in $1
):
This is especially handy on OS X, e.g., to capture a list of files sorted by creation date (oldest to newest), the ls
command is ls -t -U -r
.
This is how I do it, but there are probably more efficient ways.
TREETREE