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Top Forums Shell Programming and Scripting How do I pull a substring out of a file? Post 302331851 by enator45 on Tuesday 7th of July 2009 10:34:41 AM
Old 07-07-2009
How do I pull a substring out of a file?

I'm new to shell scripting and am trying to write a small script that pulls a substring out of a file that has a few lines of text in it. The file will eventually have a lot of text, I just put a few lines in it for testing purposes.

Anyway, this is what I have so far...

Code:
#!/bin/ksh
 
top > testlog.txt
df -h >> testlog.txt
 
freeMem=`grep ",.*free mem," testlog.txt`
home=`grep "home" testlog.txt`

echo $freeMem
echo $home

as of now, it displays the entire line that the grep's return. I want to display just a substring out of each line that's returned from the two greps.

I've tried doing it two ways, but can't get it to work. Here's an example using my freeMem var:

Way 1: echo ${freeMem:22:2}
get an error saying something like bad substitution

Way 2: freeMem=`grep -o ",.*free mem," testlog.txt`
just doesn't work for me, says I can't us -o, but google says I should be able to.

Here's an example of the line that's in testlog.txt that the grep would return:

Memory: 16G phys mem, 11G free mem, 4103M swap, 4103M free swap

I want to display only the substring "11G".

Thanks in advance for any help.
 

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Mojo::Asset::Memory(3pm)				User Contributed Perl Documentation				  Mojo::Asset::Memory(3pm)

NAME
Mojo::Asset::Memory - In-memory storage for HTTP 1.1 content SYNOPSIS
use Mojo::Asset::Memory; my $mem = Mojo::Asset::Memory->new; $mem->add_chunk('foo bar baz'); say $mem->slurp; DESCRIPTION
Mojo::Asset::Memory is an in-memory storage backend for HTTP 1.1 content. EVENTS
Mojo::Asset::Memory can emit the following events. "upgrade" $mem->on(upgrade => sub { my ($mem, $file) = @_; ... }); Emitted when asset gets upgraded to a Mojo::Asset::File object. $mem->on(upgrade => sub { my ($mem, $file) = @_; $file->tmpdir('/tmp'); }); ATTRIBUTES
Mojo::Asset::Memory inherits all attributes from Mojo::Asset and implements the following new ones. "auto_upgrade" my $upgrade = $mem->auto_upgrade; $mem = $mem->auto_upgrade(1); Try to detect if content size exceeds "max_memory_size" limit and automatically upgrade to a Mojo::Asset::File object. "max_memory_size" my $size = $mem->max_memory_size; $mem = $mem->max_memory_size(1024); Maximum size in bytes of data to keep in memory before automatically upgrading to a Mojo::Asset::File object, defaults to the value of the "MOJO_MAX_MEMORY_SIZE" environment variable or 262144. METHODS
Mojo::Asset::Memory inherits all methods from Mojo::Asset and implements the following new ones. "new" my $mem = Mojo::Asset::Memory->new; Construct a new Mojo::Asset::Memory object. "add_chunk" $mem = $mem->add_chunk('foo bar baz'); my $file = $mem->add_chunk('abc' x 262144); Add chunk of data and upgrade to Mojo::Asset::File object if necessary. "contains" my $position = $mem->contains('bar'); Check if asset contains a specific string. "get_chunk" my $chunk = $mem->get_chunk($offset); Get chunk of data starting from a specific position. "move_to" $mem = $mem->move_to('/home/sri/foo.txt'); Move asset data into a specific file. "size" my $size = $mem->size; Size of asset data in bytes. "slurp" my $string = mem->slurp; Read all asset data at once. SEE ALSO
Mojolicious, Mojolicious::Guides, <http://mojolicio.us>. perl v5.14.2 2012-09-05 Mojo::Asset::Memory(3pm)
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