UNIX for Dummies Questions & Answers

sorry - bad copy/paste:

Code:

nawk -F, -v OFS=',' -v asd='33,44' -v mnmn='55,66' '$1 == "asd" || $1 == "mnmn"  {$1= $1 OFS (($1==asd) ? asd : mnmn)}1' myFile.txt

Python alternative

Code:

#!/usr/bin/python
import fileinput
for lines in fileinput.FileInput("input.txt", inplace=1): #inplace edit
 	a = lines.strip().split(",")
 	if a[0] == "asd":
 		insertstring = ",33,44," 
 	if a[0] == "mnmn":
 		insertstring = ",55,66," 
 	print a[0] , insertstring , ','.join(a[1:])

output:

Code:

asd ,33,44, 12,12,12,12,1,2,1,1,1,1,1
mnmn ,55,66, 1,12,1,1,1,112,12,1,1,1

hi

thank u gostdog74
but i am a newer to unix
i don't know python

1. fileinput is a Python standard module for looping over files and processing them. So we import it into the script.
2. Here we loop over the lines in the file, using for loop. The "inplace = 1" argument says to perform modification to the file "without creating a temporary file", ie inplace editing.
3. Strip the line of newlines and then split them up using ',' as delimiter. Eg asd,12,12,12,12,1,2,1,1,1,1,1 will become ['asd', '12', '12', '12', '12', '1', '2', '1', '1', '1', '1', '1']. In Python , strings are immutable, do i use a list
4-7. to refer to elements of a list in Python, we use indexes. eg a[0] refers to the first element, which is "asd". The second element will be a[1] which is '12' and so on.
8. a[1:] means get from index 1 (element 2) till the end of the list.
",".join ( a[1:] ) means to join ['12', '12', '12', '12', '1', '2', '1', '1', '1', '1', '1'] back to a string 12,12,12,12,1,2,1,1,1,1,1 , using commas as delimiters.