How can I run multiple UNIX commands, using an input file, just once

Question

I'm relatively novice in Unix Shell Scripting. How can I run the (following) multiple UNIX commands (put into a script, say "discover.sh", using my_log.txt input-file just once? Eventually, I would like to create an alias [alias discover1='~/discover.sh'] in my .bashrc.

Like:

$ discover1 my_log.txt

Current script:

/bin/egrep 'Version:|Online \(warning\)|Failed \(offline\)' my_log.txt;
/bin/grep -A7 "syscontrol realmmgr" my_log.txt;
/bin/grep -C2 BIOS my_log.txt;

Why would you want that as an alias instead of creating a shell script in your $HOME/bin directory, which should be on your $PATH? There probably are ways to cat the file just once, especially in bash. I'm not sure whether they're worth using. For example: cat my_log.txt | tee >(/bin/egrep 'Version...') >(/bin/grep -A7 "...") | /bin/grep -C BIOS. This loses control over the sequencing of the output (you could get partial lines from different processes). If you really want to scan the file just once, I suggest using Perl do the searches all at once. Not quite trivial, but pretty easy. — Jonathan Leffler
– Jonathan Leffler, Commented Apr 11, 2013 at 5:46

Barmar · Accepted Answer · 2013-04-11 02:33:19Z

1

discover.sh should contain:

#!/bin/bash
/bin/egrep 'Version:|Online \(warning\)|Failed \(offline\)' "$1"
/bin/grep -A7 "syscontrol realmmgr" "$1";
/bin/grep -C2 BIOS "$1";

The variable $1 is automatically set to the first parameter of the script.

answered Apr 11, 2013 at 2:33

Barmar

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2 Comments

Jonathan Leffler Over a year ago

Any reason not to use "$@" in place of "$1"? It's more general if you process any number of files (other than zero). It isn't entirely clear that it is safe if there is no argument; arguably, the script should check that there is at least a "$1" to work on.

Barmar Over a year ago

These are both reasonable.

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