Take part of a Linux command line from a file

eddyq · 01-11-2012, 11:07 AM

I have some scripts. Each script compiles a different library and each script uses a sed string to modify the output.

e.g. gmake library | sed 's/powerpc.*[ \t]/compiling -->/'

I would like to make all scripts use the same sed string from a file so I don't have to modify each script everytime I change the sed string.

I tried putting everything after the | symbol into a file called sed_string then I tried using "<sed_string" but, as expected, that did not work.

Does anyone know how to do this?

David the H. · 01-11-2012, 11:17 AM

Suggestion one:

1) Create a function for your sed command and modify the scripts so that they use it.

2) Store the function in a separate text file.

3) Source that file into your scripts.

Suggestion two:

Use sed's ability to read expressions from a file.

Code:

sed -f filename

eddyq · 01-11-2012, 11:54 AM

I don't know how to make sed functions so I tried the -f method. It worked perfectly.

Thanks

wpeckham · 01-11-2012, 04:16 PM

IN that case might you want to mark this thread SOLVED?

David the H. · 01-12-2012, 06:26 AM

Not a sed function, a shell function, containing the sed command you want. sed itself doesn't have a function feature.

The details depend to some extent on which shell you use, but if you're using bash:

http://mywiki.wooledge.org/BashGuide...ands#Functions
http://www.tldp.org/LDP/abs/html/functions.html

And see here for some details about sourcing a file:

http://wiki.bash-hackers.org/howto/conffile

onebuck · 01-12-2012, 06:50 PM

Moved: This thread is more suitable in <Programming> and has been moved accordingly to help your thread/question get the exposure it deserves.

theNbomr · 01-13-2012, 10:14 AM

Your problem can be decomposed into two smaller problems, each with solutions.

1. You want to read stuff from a file. This reads one line from a file called sed_string, into a variable called $argVar

Code:

read argVar < sed_string
# Echo the line, just to make sure...
echo $argVar

2. You can use the variable as a commandline argument to sed. If the line read from the file might contain whitespace, you should enclose it in quotes.

Code:

sed \'${argVar}\'

You can combine these component code fragments in loops and larger code segments according to your requirements.

--- rod.

ntubski · 01-13-2012, 11:39 AM

Code:

sed \'${argVar}\'

This quoting style doesn't work:

Code:

$ echo $argVar
s/foo bar/foobar/
$ echo 'foo bar' | sed \'${argVar}\'
sed: -e expression #1, char 1: unknown command: `''
$ echo 'foo bar' | sed "${argVar}"
foobar

theNbomr · 01-13-2012, 12:46 PM

Duhhh. I only tested the quoting with an echo command. Thanks for the catch.

--- rod.

Nominal Animal · 01-14-2012, 01:12 AM

Quote:

Originally Posted by theNbomr

2. You can use the variable as a commandline argument to sed. If the line read from the file might contain whitespace, you should enclose it in quotes.

Code:

sed "${argVar}"

I agree. (theNbomr, I took the liberty to fix the quotes there).

Additionally, eddyq, if you use a Bash shell, you can compose the arguments to the command in an array first, then supply the array as the command-line parameters.

For example, you might wish to use a sed command, which takes the regular expressions from one source, edit mode options from another, and file names from third source:

Code:

#!/bin/bash

# Keep all non-ASCII characters intact, regardless of the charset.
export LANG=C LC_ALL=C

# This will contain the command line arguments for sed.
# Note that "${args[@]}" means "each separate item in args".
args=()

# Add a pattern that changes each 'foo' to 'bar'.
args=("${args[@]}" -e 's|foo|bar|g')

# Add a pattern which removes lines that begin with a # or a ;.
args=("${args[@]}" -e '/^[\t\v\f\r ]*#/ d')

# Add option -i which tells sed to edit the target files in-place,
# instead of outputting the changes to standard output.
args=("${args[@]}" -i)

# Add everything supplied on the command line to this script, too.
# (Basically, assume they're all file names or sed options.)
args=("${args[@]}" "$@")

# Execute the sed command, using parameters defined above.
sed "${args[@]}"

As you can see, this is quite easy to use, and allows you to construct very complex commands without relying on tedious if-then or case-esac structures.

Do note, however, that input and output redirections ( <input-file and >output-file ) are handled by the shell, not the command itself, so you cannot do redirections by inserting those into the array.