Frequently I need to run a process for each item in a list, stored in a text file one item per line: usernames, filenames, e-mail addresses, etc. Obviously there are more than 3 ways to do this, but here are 3 I have found useful:<\/p>\n
Bash<\/strong> Source: prog1.sh<\/strong><\/p>\n 4 lines. Not bad.<\/p>\n Perl<\/strong> Source: prog2.pl<\/strong><\/p>\n 3 lines. Pretty good.<\/p>\n Perl -n<\/strong> Source: prog3.pl<\/strong><\/p>\n 1 line! The I really like this method because you can write a script that processes a single input that could easily be reused by another script, but can also easily be used to process an entire list by adding just the I should note that in the examples above, I am using As suggested by a comment on a previous post, I have made these examples available in a git repository: iterate over lines<\/a>. <\/p>\n","protected":false},"excerpt":{"rendered":" Frequently I need to run a process for each item in a list, stored in a text file one item per line: usernames, filenames, e-mail addresses, etc. Obviously there are more than 3 ways to do this, but here are 3 I have found useful: Bash sh prog1.sh list.txt Source: prog1.sh while read line do … Continue reading 3 ways to iterate over lines of a file in Linux<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[92,232],"tags":[197,360],"class_list":["post-1562","post","type-post","status-publish","format-standard","hentry","category-perl","category-tips-tricks","tag-bash","tag-perl"],"_links":{"self":[{"href":"https:\/\/osric.com\/chris\/accidental-developer\/wp-json\/wp\/v2\/posts\/1562","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/osric.com\/chris\/accidental-developer\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/osric.com\/chris\/accidental-developer\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/osric.com\/chris\/accidental-developer\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/osric.com\/chris\/accidental-developer\/wp-json\/wp\/v2\/comments?post=1562"}],"version-history":[{"count":12,"href":"https:\/\/osric.com\/chris\/accidental-developer\/wp-json\/wp\/v2\/posts\/1562\/revisions"}],"predecessor-version":[{"id":1575,"href":"https:\/\/osric.com\/chris\/accidental-developer\/wp-json\/wp\/v2\/posts\/1562\/revisions\/1575"}],"wp:attachment":[{"href":"https:\/\/osric.com\/chris\/accidental-developer\/wp-json\/wp\/v2\/media?parent=1562"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/osric.com\/chris\/accidental-developer\/wp-json\/wp\/v2\/categories?post=1562"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/osric.com\/chris\/accidental-developer\/wp-json\/wp\/v2\/tags?post=1562"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\nsh prog1.sh list.txt<\/code><\/p>\nwhile read line\r\ndo\r\n echo $line\r\ndone < $1<\/code><\/pre>\n
\nperl prog2.pl list.txt<\/code><\/p>\nwhile(<>) {\r\n print `echo $_`;\r\n}<\/code><\/pre>\n
\nperl -n prog3.pl list.txt<\/code><\/p>\nprint `echo $_`;<\/code><\/pre>\n-n<\/code> switch basically wraps your Perl code in a loop that processes each line of the input file. I just discovered this while flipping through my 17-year-old copy of Programming Perl<\/a><\/em> (link is to a newer edition).<\/p>\n-n<\/code> switch. (There’s also a similar -p<\/code> switch that does the same thing, but additionally prints out each line.)<\/p>\necho<\/code> as a substitute for any command external to the script itself. In the Perl examples, there would be no need to call echo<\/code> to merely print the contents of the line, but it’s a convenient stand-in for a generic command.<\/p>\n