49 lines
2.3 KiB
Markdown
49 lines
2.3 KiB
Markdown
---
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author: einar
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comments: true
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date: 2007-05-06 08:40:21+00:00
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layout: page
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slug: useful-command-line-tips
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title: Useful command line tips
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wordpress_id: 244
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categories:
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- Linux
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---
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While working through large text files for work, I found several command line tools whose existence was unknown to me before. Their usefulness is great however, expecially if you deal with comma or tab delimited files (I do, and a great deal).
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For example you can cut specific columns out of a file with the cut command:
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[code lang='c']
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cut -f [fieldname] textfile
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[/code]
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You can also specify ranges (-f1,5) or a starting point till the end (-f2,. By default the field delimiter is TAB but you can change it with the -d option:
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[code lang='c']
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cut -d , -f1,2 textfile
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[/code]
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By default it outputs the result to the standard output, so you will need to redirect (>) to a file if needed. The --output-delimiter option permits you to change the delimiter of the output.
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The paste command does exactly the reverse:
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[code lang='c']
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paste file1 file2 > resultfile
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[/code]
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Basically it adds file2's lines to file1's, useful if you have to add a specific column from another file.
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Another nice utility is the "comm" command. I recently found it and it's a life saver if you have two files that contain similar elements and you want to find out which are common and which aren't. As a prerequisite the files should be **sorted** first, otherwise you won't get the right results. Then you can use comm to print out a series of information.
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[code lang='c']
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sort file1 > file1.sorted
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sort file2 > file2.sorted
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comm -13 file1.sorted file2.sorted
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[/code]
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In this particular example I tell comm to suppress output of the lines that are only in the first file (-1) and the common lines (-3) so that you effectively get only file2's items. The other option is -2, and that suppresses lines unique from file2. Again the output is on standard output so if you need to save it you'll have to redirect it somewhere.
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That's all for now. As you can see the command line can do a few interesting things (try that, cmd.exe) and that's merely the surface (google for other powerful commands such as awk or sed and you'll see what I mean). By doing things this way I manage my files far more efficiently than with a GUI.
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