The three commands can be used to process the text/message. Usually, grep is used to filter lines containing the keyword. cut is used to output part of the line. awk is used to modify the lines.

grep

The common usage of grep to find keyword is as follows.

fool@bar:~$ grep "keyword" ./file.txt

• -n: print the line number
• -i: ignore case distinctions
• -w: match whole the words
• -o: output only the matching segment, rather than the full line
• -E: use extended regular expression syntax
• -C2: show 2 context lines in addition to the matched line

cut

The common usage of cut to split a line by spaces and select the first field is as follows.

fool@bar:~$ cut -d " " -f 1 ./file.txt

• -d " " -f 1, 2 ----output-delimiter='%': use space as delimiter and select the first and the second fields of each line and output with delimiter %.
• -b 1-5: select the first to the fifth byte of each line
• -c 1, 2: select the first and the second character of each line

awk

The common usage of awk to split a line containing the keyword by spaces and select the first field is as follows.

fool@bar:~$ awk '/keyword/ {print $1}' ./file.txt

fool@bar:~$ awk '{print "newstring " $1,$4}' employee.txt