help with grep

[dunryc]

HI guys

Hopefully some one more informed than me will no ?

is there any way to use grep ( or any other command ) to give me lines starting with in a text file so

display all commands starting with a I have searched the net but seem unable to find any pertinent results !!

Here's hoping cheers guys

[DaithiF]

Hi, you want to search a file for lines which begin with a certain pattern? (not completely clear from your post).

lets say you want to find lines starting with 'a'. some examples:


grep "^a" somefile # match lines where 1st character is a
grep "^\s*a" somefile # match lines where 1st non-whitespace character is a
grep -i "^\s*a" somefile # match lines where 1st non-whitespace character is a or A

[dunryc]

that great erally appreciate it

thanks :D

[libssd]

Not quite what you asked for, but this lists all lines that contain a specific string (in this example, the word source ):


$ cat *.txt | grep source
4. Re-add remastersys and medibuntu to Synaptic sources.
sudo gedit /etc/apt/sources.list
# Source: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/560464
Various sources, including: https://help.ubuntu.com/community/AA1/Using

Terminal screenshot attached, showing color mapping.

[libssd]

Even easier: use look

This finds lines beginning with Source (but not beginning with source):


$ look Source *.txt
Source: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/560464
Source: http://www.webupd8.org/2010/04/install-nautilus-elementary-230-via-ppa.html





LOOK(1) BSD General Commands Manual LOOK(1)

NAME
look — display lines beginning with a given string

SYNOPSIS
look [-bdf] [-t termchar] string [file ...]

[DaithiF]

Even easier: use look


no, read the next part of the manpage:


DESCRIPTION
The look utility displays any lines in file which contain string as a
prefix. As look performs a binary search, the lines in file must be
sorted

look is intended for looking up words in dictionaries (where the words are sorted), its not a general purpose grep-replacement.

[libssd]

look is intended for looking up words in dictionaries (where the words are sorted), its not a general purpose grep-replacement.
I understand that's what look is intended for, but in fact, look appears to work as I described. Before posting, I used it against a text file to check.

[DaithiF]

no it doesn't. for unsorted files it will occasionally match what you are looking up, when its binary search mechanism happens to chance upon a matching line. but mostly it won't.

to illustrate -- the following uses look to first try to match each line of an unsorted file, then does the same for a sorted version.

$ cat testfile
this
is
a
file
with
various
lines
of
text

$ while read line; do echo "testing '$line'"; look "$line" testfile; done < testfile
testing 'this'
testing 'is'
testing 'a'
testing 'file'
file
testing 'with'
testing 'various'
testing 'lines'
testing 'of'
of
testing 'text'
text

$ sort testfile > testfile.sorted

$ while read line; do echo "testing '$line'"; look "$line" testfile.sorted; done < testfile.sorted
testing 'a'
a
testing 'file'
file
testing 'is'
is
testing 'lines'
lines
testing 'of'
of
testing 'text'
text
testing 'this'
this
testing 'various'
various
testing 'with'
with

[libssd]

Thanks for taking the time for the explanation and examples, which describe the correct way to get the desired result using grep.