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[[Category:Tips]] Often you will want to automate certain commands with BASH. The easiest way to do this is by using file globbing with wildcards otherwise called expansion. For example say I have a directory with the following files in it $ ls file1.txt file2.txt file3.txt If I type $ ls *.txt file1.txt file2.txt file3.txt The Shell will expand *.txt to match any file that matches the pattern of any number of characters followed by a .txt it then sends this list to the ls command. The ls command takes that list as a set and displays the directory listing for each one. Now most commands will work with file globbing but sometimes there are problems. For example if I wish to convert a heap of .jpeg files to 800x600 resolution with one line: $ ls *.jpeg img_2992.jpeg img_2994.jpeg img_2996.jpeg img_2998.jpeg img_3000.jpeg img_3002.jpeg img_2993.jpeg img_2995.jpeg img_2997.jpeg img_2999.jpeg img_3001.jpeg $ convert *.jpeg -resize 800x600 *.jpeg $ ls *.jpeg img_2992.jpeg img_2998.jpeg img_3002-10.jpeg img_3002-16.jpeg img_3002-3.jpeg img_3002-9.jpeg img_2993.jpeg img_2999.jpeg img_3002-11.jpeg img_3002-17.jpeg img_3002-4.jpeg img_3002.jpeg img_2994.jpeg img_3000.jpeg img_3002-12.jpeg img_3002-18.jpeg img_3002-5.jpeg img_2995.jpeg img_3001.jpeg img_3002-13.jpeg img_3002-19.jpeg img_3002-6.jpeg img_2996.jpeg img_3002-0.jpeg img_3002-14.jpeg img_3002-2.jpeg img_3002-7.jpeg img_2997.jpeg img_3002-1.jpeg img_3002-15.jpeg img_3002-20.jpeg img_3002-8.jpeg Of course that was not what we expected. There is an easier solution to this and that is to use BASH's for loop command. $ for var1 in *.jpeg; do convert $var1 -resize 800x600 $var1; done $ ls *.jpeg img_2992.jpeg img_2994.jpeg img_2996.jpeg img_2998.jpeg img_3000.jpeg img_3002.jpeg img_2993.jpeg img_2995.jpeg img_2997.jpeg img_2999.jpeg img_3001.jpeg What this command does is loop through all the .jpeg files in the directory and for each file it stores the name of that file in the variable $var1 which is then used as two arguments to convert, the input and output file names respectively. Basically it looks to the system like this convert img_2992.jpeg -resize 800x600 img_2992.jpeg convert img_2993.jpeg -resize 800x600 img_2993.jpeg convert img_2994.jpeg -resize 800x600 img_2994.jpeg convert img_2995.jpeg -resize 800x600 img_2995.jpeg convert img_2996.jpeg -resize 800x600 img_2996.jpeg convert img_2997.jpeg -resize 800x600 img_2997.jpeg convert img_2998.jpeg -resize 800x600 img_2998.jpeg convert img_2999.jpeg -resize 800x600 img_2999.jpeg convert img_3000.jpeg -resize 800x600 img_3000.jpeg convert img_3001.jpeg -resize 800x600 img_3001.jpeg convert img_3002.jpeg -resize 800x600 img_3002.jpeg You can play with this by echoing the output of the expansion to the console. $ for var2 in *.txt; do echo $var2 ;done file1.txt file2.txt file3.txt $ echo *.txt file1.txt file2.txt file3.txt Those are similar expansions but not exactly the same. Note: var1 and var2 are random variable names that I have picked. You can use other variable names like images or textfiles.

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