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Top Forums UNIX for Dummies Questions & Answers Scripting Question (For Loop) Post 302953021 by neutronscott on Tuesday 25th of August 2015 01:36:49 AM
Old 08-25-2015
Quote:
Originally Posted by shah9250
However, what do you mean by properly split list of files?
See the following shell session example:

Code:
mute@tiny:~$ mkdir shah9250
mute@tiny:~$ cd shah9250/
mute@tiny:~/shah9250$ touch 'file with spaces'
mute@tiny:~/shah9250$ for f in $(ls); do echo "work on [$f]"; done
work on [file]
work on [with]
work on [spaces]
mute@tiny:~/shah9250$ for f in *; do echo "work on [$f]"; done
work on [file with spaces]

We know there is only one file and the loop should only be called once, but with that use of $(ls) it's not. Quoting and word splitting are the toughest parts of learning the shell, in my opinion. Once that clicks things are much easier.

Quote:
Originally Posted by shah9250
Also what is a glob? Also you used a wildcard (*) in the "for" statement, so how does the variable $file receive input?
Glob is filename expansion. * is a wildcard that matches anything. You can simply do echo * or echo *.txt to show all files or all files ending in .txt. My meaning wasn't to distract from the for loop, just for down the road you'll want to use best practices. Filenames can contain any character except the NUL character and the path delimiter / and a great deal of care must be taken to make robust scripts.

I cannot recommend Greg's wiki enough. The bash guide on the site is excellent value for the price: BashGuide - Greg's Wiki
This User Gave Thanks to neutronscott For This Post:
 

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SHELL-QUOTE(1p) 					User Contributed Perl Documentation					   SHELL-QUOTE(1p)

NAME
shell-quote - quote arguments for safe use, unmodified in a shell command SYNOPSIS
shell-quote [switch]... arg... DESCRIPTION
shell-quote lets you pass arbitrary strings through the shell so that they won't be changed by the shell. This lets you process commands or files with embedded white space or shell globbing characters safely. Here are a few examples. EXAMPLES
ssh preserving args When running a remote command with ssh, ssh doesn't preserve the separate arguments it receives. It just joins them with spaces and passes them to "$SHELL -c". This doesn't work as intended: ssh host touch 'hi there' # fails It creates 2 files, hi and there. Instead, do this: cmd=`shell-quote touch 'hi there'` ssh host "$cmd" This gives you just 1 file, hi there. process find output It's not ordinarily possible to process an arbitrary list of files output by find with a shell script. Anything you put in $IFS to split up the output could legitimately be in a file's name. Here's how you can do it using shell-quote: eval set -- `find -type f -print0 | xargs -0 shell-quote --` debug shell scripts shell-quote is better than echo for debugging shell scripts. debug() { [ -z "$debug" ] || shell-quote "debug:" "$@" } With echo you can't tell the difference between "debug 'foo bar'" and "debug foo bar", but with shell-quote you can. save a command for later shell-quote can be used to build up a shell command to run later. Say you want the user to be able to give you switches for a command you're going to run. If you don't want the switches to be re-evaluated by the shell (which is usually a good idea, else there are things the user can't pass through), you can do something like this: user_switches= while [ $# != 0 ] do case x$1 in x--pass-through) [ $# -gt 1 ] || die "need an argument for $1" user_switches="$user_switches "`shell-quote -- "$2"` shift;; # process other switches esac shift done # later eval "shell-quote some-command $user_switches my args" OPTIONS
--debug Turn debugging on. --help Show the usage message and die. --version Show the version number and exit. AVAILABILITY
The code is licensed under the GNU GPL. Check http://www.argon.org/~roderick/ or CPAN for updated versions. AUTHOR
Roderick Schertler <roderick@argon.org> perl v5.8.4 2005-05-03 SHELL-QUOTE(1p)
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