Session6.md

Regex applications

Note: All these commands follow GNU sed's standard

Use of sed for stream editing of text

Use np to print the nth line

  sed '5p' RollList.csv

Note: The output might slightly differ from what you'd expect. To understand why, keep reading $^\dagger$.

Use of x,yp to print a range of lines

  sed '2,9p' RollList.csv

Use /your_regex_here/p to print lines that match the regular expression

  sed '/ME/p' RollList.csv
  
  sed '/ME/!p' RollList.csv     *prints all the lines that do not match the regular expression*

Use -n to supress pattern space $^\dagger$

  sed -n '/ME/p' RollList.csv

Strip the roll number

  sed -n 's/....B...,//p' RollList.csv

Strip the name

  sed -n 's/,.*//p' RollList.csv

Use of sed to edit a stream of lines

  cat RollList.csv | sed -e 's/^.*,//g'

  cat RollList.csv | sed -e 's/^.*,//g' > n.txt

  cat RollList.csv | sed -e 's/,.*//g' > r.txt

Use of brackets to store fields (capturing groups)

  cat RollList.csv | sed -e 's/^\(.*\),\(.*\)$/\2,\1/g'

Changing case of fields

  cat RollList.csv | sed -e 's/^\(.*\),\(.*\)$/\2,\L\1/g'

Changing case of fields and adding text that makes the roll number appear as an email address.

  cat RollList.csv | sed -e 's/^\(.*\),\(.*\)$/\2,\L\1@smail.iitm.ac.in/g'