Shell Utilities

Shell Utilities

1. Linux provides tools, and mechanisms, like the pipe, to put these tools together into useful utilities.

   • cat
     • cat stands for 'concatenation', cat takes a number of files and display them together
       • cat fruits.txt = cat < fruits.txt
       • cat fruits.txt vegetables.txt
       • cat fruits.txt vegetables.txt >> fruitsAndVegetables.txtx
       • cat > myFile.txt (writes data into the file)
   • head, tail
     • These commands are used to viewing large files
       • head myFile.txt #displays the first 10 line of the file myFile.txt
       • tail myFile.txt #display the last 10 lines of the file myFile.txt
       • head -2 myFiles.txt (shows the first 2 lines)
         • You can combine the cat and the head/tail commands: cat fruits.txt | head -3
   • more
     • The more command to view large files, one page at time.
       • On most linux systems, more can also be called 'less'.
         • more a_large_file.txt
         • man ls | more
         • Use PageUp/PageDown or 'f' and 'q' to move forward or back a page, and q to exit the view mode (and 'h' to get help)
   • lpr
     • This command is used to send a file to a printer, lpr stands for line printer
       • lpr myFile.txt # sends the file myFile.txt to the default printer
       • cat another_file.txt | lpr
       • lpr < fruits.txt
       • lpr -PmyPrinter fruits.txt #sends the file fruits.txt to the printer myPrinter
     • lpq
       • Displays the queue of the default printer, we can use the -P option to display the job of an specific printer.
         • lpq
         • lpq -PmyPrinter
       • lprm
         • Removes a nominated job (use the number in the job column of the lpq output)
           • lprm 14 (removes the job 14)
   • cut
     • Print selected parts of lines from each FILE to standard output (cuts out)
       • echo "123abc" | cut -c 3-5 (get the characters from 3 to 5 index: 3ab)
       • cut -d " " -f 1 myFile.txt (gets the first field from the file delimited by a space, d=delimiter, f=fields)
   • tr
     • This command is used to translate characters and remove unwanted characters
       • echo "abcd" | tr 'a-z' 'A-C' = ABCD
       • echo "abcd" | tr -d "aiueo" (deletes all the vowels) = bcd
       • echo "abcd" | tr -dc "aiueo\n" (ingnores everything except the vowels and the ENTER) = a