Common text edit tools

refer to linux foundation from Edx:

Command Usage
cat file1 file2 Concatenate multiple files and display the output; i.e., the entire content of the first file is followed by that of the second file.
cat file1 file2 > newfile Combine multiple files and save the output into a new file.
cat file >> existingfile Append a file to the end of an existing file.
cat > file Any subsequent lines typed will go into the file until CTRL-D is typed.
cat >> file Any subsequent lines are appended to the file until CTRL-D is typed.

The tac command (cat spelled backwards) prints the lines of a file in reverse order. (Each line remains the same but the order of lines is inverted.) The syntax of tac is exactly the same as for cat as in

Command Usage
echo string > newfile The specified string is placed in a new file.
echo string >> existingfile The specified string is appended to the end of an already existing file.
echo $variable The contents of the specified environment variable are displayed.

$ less <filename>
$ cat <filename> | less

head reads the first few lines of each named file (10 by default) and displays it on standard output. You can give a different number of lines in an option

$ head –n 5 atmtrans.txt

tail prints the last few lines of each named file and displays it on standard output. By default, it displays the last 10 lines.

$ tail -n 15 atmtrans.txt

Command Description
$ zcat compressed-file.txt.gz To view a compressed file
$ zless <filename>.gz
or
$ zmore <filename>.gz
To page through a compressed file
$ zgrep -i less test-file.txt.gz To search inside a compressed file
$ zdiff filename1.txt.gz
filename2.txt.gz
To compare two compressed files
Command Usage
sed -e command <filename> Specify editing commands at the command line, operate on file and put the output on standard out (e.g., the terminal)
sed -f scriptfile <filename> Specify a scriptfile containing sed commands, operate on file and put output on standard out.
Command Usage
sed s/pattern/replace_string/ file Substitute first string occurrence in a line
sed s/pattern/replace_string/g file Substitute all string occurrences in a line
sed 1,3s/pattern/replace_string/g file Substitute all string occurrences in a range of lines
sed -i s/pattern/replace_string/g file Save changes for string substitution in the same file

You must use the -i option with care, because the action is not reversible. It is always safer to use sed without the –i option and then replace the file yourself, as shown in the following example:

$ sed s/pattern/replace_string/g file1 > file2

The above command will replace all occurrences of pattern with replace_string in file1 and move the contents tofile2. The contents of file2 can be viewed with cat file2. If you approve you can then overwrite the original file with mv file2 file1.

Example: To convert 01/02/… to JAN/FEB/…
sed -e ‘s/01/JAN/’ -e ‘s/02/FEB/’ -e ‘s/03/MAR/’ -e ‘s/04/APR/’ -e ‘s/05/MAY/’ \
-e ‘s/06/JUN/’ -e ‘s/07/JUL/’ -e ‘s/08/AUG/’ -e ‘s/09/SEP/’ -e ‘s/10/OCT/’ \
-e ‘s/11/NOV/’ -e ‘s/12/DEC/’

awk

awk is used to extract and then print specific contents of a file and is often used to construct reports.

awk is invoked as shown in the following:

Command Usage
awk ‘command’ var=value file Specify a command directly at the command line
awk -f scriptfile var=value file Specify a file that contains the script to be executed along with f

As with sed, short awk commands can be specified directly at the command line, but a more complex script can be saved in a file that you can specify using the -f option.

The table explains the basic tasks that can be performed using awk. The input file is read one line at a time, and for each line, awk matches the given pattern in the given order and performs the requested action. The -F option allows you to specify a particular field separator character. For example, the /etc/passwd file uses : to separate the fields, so the -F: option is used with the /etc/passwd file.

The command/action in awk needs to be surrounded with apostrophes (or single-quote (‘)). awk can be used as follows:

Command Usage
awk ‘{ print $0 }’ /etc/passwd Print entire file
awk -F: ‘{ print $1 }’ /etc/passwd Print first field (column) of every line, separated by a space
awk -F: ‘{ print $1 $6 }’ /etc/passwd Print first and sixth field of every line
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