While creating websites I often find the need to manipulate files in all sorts of ad-hoc ways.
Things that are hard to do by hand, but you don’t want to write a whole program for - you’ll just use it once and throw it away.
Linux/Unix excels at this sort of task - there is a rich selection of tools and plenty of ready made recipes.
I often use
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http://student.northpark.edu/pemente/sed/sed1line.txt gives me a way to print out just the lines near an error is being generated (handy when there is one error line in a gigabyte of data)
Though day to day grep, find, locate and thier friends usually do all I need.
I tried working on Windows a while ago - but found I just couldn’t work effectively without these tools.