Difference between revisions of "Using awk grep sed"

Latest revision as of 16:08, 23 February 2022

grep does not alter a file, it only finds matches while awk and sed are text processors.

awk is mostly used for data extraction and reporting. sed is a stream editor. Each one of them has its own functionality and specialties.

sed

Stream EDitor (sed). Things that you can accomplish using RegEx within the Vi editor on text files can also be accomplished at the command line with sed.

sed -i 's/old-text/new-text/g' input.txt

• s is the substitute
• -i flag, tells sed to update the file
• g/ means global replace

The most basic form is to use sed as a simple search and replace.

sed 's/windows/linux/'

example: process text file by removing blanks, unwanted lines, and duplicates

Get rid of all lines of text containing numerical stats

sed -i '/[0-9]/d' Razor-Fen.txt

Get rid of all empty lines containing no characters

sed -i '/^\s*$/d' Razor-Fen.txt

Get rid of all duplicate lines

sed -i '$!N; /^\(.*\)\n\1$/!P; D' Razor-Fen.txt

example: edit each line of text with character removal or substitution

Just like we would edit lines of text using vim, we can use sed to make modifications on a line by line basis. In this example we are going to process a text file and remove part of each line containing information that we do not need. If we were in the vim editor it would look like this:

:%s/\[202.*PlayerID:\ //

To mimic this using sed it will look like this:

sed -E 's/\[202.*PlayerID:\ //' playerids.txt > playerids2.txt

The output file contains the same number of lines, with each line having had a portion removed.

example: cat, head, and tail displaying a portion of a text file

If you have a large text file and wish to display only a portion of the file from within (the center)

sed -n '5001,6000p' largetextfile.txt

starts at line 5001 and ends at line 6000.

This would be similar to the following examples

head -n6000 largetextfile.txt | tail -n1000
tail -n5001 largetextfile.txt | head -n1000

With sed you can grab text from the middle without having to pipe.

grep

example: rgrep

rgrep is grep -r or recursive grep

If you want to search all text files within all subfolders for a particular matching string, the syntax might not be what you would think

For example, rgrep string *.txt will not search though all text files under the current directory, the correct syntax would be:

rgrep -s string --include \*.txt

Here is an example that searches for multiple specific types

rgrep -i --include \*.h --include \*.cpp CP_Image ~/path[12345]

awk

The awk utility operates on a line-by-line basis and iterates through the entire file and is therefore useful for changing data files and generating reports.

This command utility is extremely useful for formatting text to the screen or for print. You can process huge log files to output a readable report that you can better utilize.

Format:

awk '/pattern/ { action_to_take; another_action; }' file_to_parse

By default Awk behaves like 'cat' in that it prints every line of data from the specified file.

awk '{print}' inventory.txt

GNU Awk has the option of "inplace" file editing since 4.1.0

awk -i inplace 'BEGIN { FS="/"; } {print $2}' /tmp/biomes.txt

picking out specific lines in the data or text file

We might have a space separated data file or a text file with lines of composition, either way, we can pick out and print entire lines of text if a single word in the line is matched.

awk '/plumbing/ {print}' inventory.txt 

In the inventory file there is a second column of text that specifies the department of the listed supply item. Only lines from the text file will be printed if the item is in the plumbing department. Alternatively, if it is a composition, only lines where the word 'plumbing' is matched will be printed.

unique lines only without changing sort order

Isolate all of the unique lines from the text file.

awk '!seen[$0]++' playeridsduplicates.txt > playerids.txt

If you want them sorted, or are interested in an alternative way of producing only unique lines of text, see: uniq

Related Pages

• Advanced Shell Operations
• How to write a shell script