Alternation operator

The alternation operator is used to specify alternatives. The alternation operator is a vertical bar or pipe symbol, it matches one regular expression out of several regular expressions. The '|' alternation operator has the lowest precedence among all the regular expression operators. For example, in the employee database, if we want to print the lines that have first name of the employee as Emily, Jack, or Ana, we can write the following regular expression:

$ awk '/Emily|Jack|Ana/' emp.dat

In AWK, it is generally used with the ( ) grouping operator, as follows:

$ awk '/(Emily|Jack|Ana)/' emp.dat

The output on execution of the given code is as follows:

Jack    Singh   9857532312  jack@gmail.com      M   hr      2000
Ana     Khanna  9856422312  anak@hotmail.com    F   Ops     2700
Emily   Kaur    8826175812  emily@gmail.com     F   Ops     2100

With the alternation operator, we can combine multiple regular expressions together, as follows:

$ awk '/^J|^V/' emp.dat

The output on execution of the preceding code is as follows:

Jack    Singh   9857532312  jack@gmail.com      M   hr      2000
Jane    Kaur    9837432312  jane@gmail.com      F   hr      1800
Julie   Kapur   8826234556  julie@yahoo.com     F   Ops     2500
Victor  Sharma  8826567898  vics@hotmail.com    M   Ops     2500
John    Kapur   9911556789  john@gmail.com      M   hr      2200
Vina    Singh   8811776612  vina@yahoo.com      F   lgs     2300 

So, in the previous example, we could print the employee details for those whose first name begins with J or V.

The alternation applies to the largest possible regular expressions on either side. For example, if we want to print the lines that begin with either J or V, or the email ID of users beginning with v, as follows:

$ awk '/(^J|^V)|($4 ~ ^v)/' emp.dat

The output on execution of the preceding code is as follows:

Jack    Singh   9857532312  jack@gmail.com      M   hr      2000
Jane    Kaur    9837432312  jane@gmail.com      F   hr      1800
Julie   Kapur   8826234556  julie@yahoo.com     F   Ops     2500
Victor  Sharma  8826567898  vics@hotmail.com    M   Ops     2500
John    Kapur   9911556789  john@gmail.com      M   hr      2200
Vina    Singh   8811776612  vina@yahoo.com      F   lgs     2300