Toying Common Linux Tools

# grep, egrep, cut, sed, sort, uniq, diff, awk

grep

Used to search for a specific string or pattern in a file or multiple files.

Example: grep "error" log.txt # searches for the string "error" in the file log.txt

grep -rnw '/path/to/somewhere/' -e 'pattern'
-r or -R is recursive,
-n is line number, and
-w stands for match the whole word.
-l (lower-case L) can be added to just give the file name of matching files.
-e is the pattern used during the search

grep | cut: grep can be used in combination with cut to extract specific columns from the output of grep.
Example: grep "error" log.txt | cut -d " " -f 1,3 # extract the 1st and 3rd fields from the output of grep

function seek { 
 if [ "$1" == "" ] # not specified 
 then
  echo 'Search key word required'
  echo "Usage : $0 seek $1"
 else
  echo $1
  GREP_COLORS='ms=01;32' egrep -inr --color=always $1 $2; # $2 := path_start
 fi;


 time_stamp=$(date +"%Y-%m-%d_%H%Mhr_%S"sec); 
 
 echo $time_stamp; 
}

# invert the match using the -v flag:
# print every line in the log.txt, except those lines matching the pattern `INFO`. -i indicates case insensitive.
grep -vi "INFO" log.txt

egrep (extended grep)

A variation of the grep command that supports additional regular expression syntax. It is used to search for a specific pattern in a file or multiple files.

# search for multiple patterns at once.
Example: egrep "error|warning" log.txt searches for…