Miscellaneous commands
This article will present various miscellaneous commands tested in Linux (running SuSE 10.1). Most of these will be simple command line tools. Eventually, many of these will have their own article. For now, they are presented as is with absolutely no guarantee and zero responsibility on my part if they cause loss of information or files. Use at your own risk.
Contents
Bulk image resize
If you are like me and have a high resolution digital camera, it is often necessary to resize the images before emailing them to friends and family. It is, of course, possible to manually resize them using Adobe Photoshop, The Gimp, or any other image editing programme. However, it is possible to automate this task using simple command line tools.
For an example, say you want to resize all of the jpeg images in your current directory to 800x600 and place them in a sub-directory called, "resized". Then you would execute the following commands:
find . -maxdepth 1 -name '*.jpg' -type f -exec convert -resize 800x600 {} resized/{} \;
It is also possible to have the above commands run recursively through a directory and its sub-directories like so:
find . -follow -name '*.jpg' -type f -exec convert -resize 800x600 {} ../resized/{} \;
Note that the programme convert is part of the ImageMagick suite and you will need to have it installed to use the above commands (it is, by default, in SuSE Linux).
Tracking down large files
Sometimes it is necessary to find files over a certain size and it can be somewhat tedious ls-ing through your many directories. The following command will list only those files over a certain size and only within the specified directory (and sub-directories):
find some_directory/ -size +2000k -ls
which will only list files over 2000 kb (2 MB).
Finding files containing a string in a directory hierarchy
In this example, all .php files will be searched for the string "MySQL" (case-insensitive with -i) and the line numbers will also be returned (using -n):
find . -name '*.php' -type f | xargs grep -n -i 'MySQL'
Selecting random lines from a file
This example could be used for printing random quotes from a file:
FILE="/some/file_name"; nlines=$(wc -l < "$FILE"); IFS=$'\n'; array=($(<"$FILE")); echo "${array[$((RANDOM%nlines))]}"
Here, nlines holds the total number of lines in the file. The file is read into an array (note the use of IFS — this splits the lines based on '\n'). Then, once the array has been populated, print a random line from it.
Printing a block of text from a file
Say you have a file, foo, and it contains the following lines (note the captial letters and the full stop in line six):
one blah blah Two blah blah three blah blah 3, 4 Four blah blah five blah blah 5, 6 six blah blah.
If you only want to print out lines 3, 4, and 5, execute the following command:
awk "/three/,/five/" < foo
If you only want to print out lines starting with a capital "F", execute the following command:
awk "/^F/" < foo
If you only want to print out lines ending in a full stop, execute the following command:
awk "/\.$/" < foo
Finally, if you only want to print out lines containing the numbers "5" and "6", execute the following command:
awk "/[5-6]/" < foo
