A shell script is a code (script) written for the shell or command line interpreter of an operating system such as Unix. It allows users to automate tasks which would be cumbersome to execute manually. For example renaming 2000 files. You could do it by 2000 mv commands or write up a 3 line shell script to do it for you.<\/p>\n\n\n\n
A shell script can be written in any shell scripting language installed on the system. The most widely used shell is the Bash Shell. Others include csh, ksh, tcsh, etc. Here we would only be discussing bash shell.<\/p>\n\n\n\n
Which shell I am running?<\/strong><\/p>\n\n\n\n This command would print the name of the shell you are running.<\/p>\n\n\n\n How do I switch to Bash Shell?<\/strong><\/p>\n\n\n\n Which shells are installed on my system?<\/strong><\/p>\n\n\n\n First Example<\/strong><\/p>\n\n\n\n A shell can script can be run on commandline from a file. You can use any text editor which doesn’t insert formatting into text to write a shell script. vi and emacs are good editors. Save the following code in file called test.sh:<\/p>\n\n\n\n By convention, shell scripts are saved with .sh extension. Change permissions of the file:<\/p>\n\n\n\n You can use any one of the following commands to execute your bash script.<\/p>\n\n\n\n Bash uses two kinds of variables<\/p>\n\n\n\n To see a list of system variables type:<\/p>\n\n\n\n This would give you a list of system variables. DO NOT change values of any of these variable unless you know what you are doing. Unlike Microsoft windows, Linux allows you more control over you system assuming that you know what you are doing. So, if the root granted you a rather unrestrictive access, you can create many problems for yourself.<\/p>\n\n\n\n To create a user defined variable ‘number’, for example:<\/p>\n\n\n\n You can use alphanumeric characters and underscore to for variable names. Variable names are case-sensitive. You many not use spaces in assignment. Following are not allowed.<\/p>\n\n\n\n To assign NULL values:<\/p>\n\n\n\n To print variables<\/p>\n\n\n\n Example<\/strong><\/p>\n\n\n\n Suppose you have 2000 photos in a directory and you need to rename them. The files are named as:<\/p>\n\n\n\n We need to rename them as follows:<\/p>\n\n\n\n Here is how:<\/p>\n\n\n\n j in is the counter. Line 5 increments j. s is a string. Line 4 uses the mv command renaming each file to the desired combination of text and number. Line 6 prints a message on the command line. Note that in line 3, we only loop through files ending in .JPG.<\/p>\n\n\n\n The following code show how to get a substring:<\/p>\n\n\n\n output<\/strong><\/p>\n\n\n\n A shell script is a code (script) written for the shell or command line interpreter of an operating system such as Unix. It allows users to automate tasks which would be cumbersome to execute manually. For example renaming 2000 files. You could do it by 2000 mv commands or write up a 3 line shell […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101,34],"tags":[94,35],"class_list":["post-710","post","type-post","status-publish","format-standard","hentry","category-bash","category-linux","tag-bash","tag-linux"],"_links":{"self":[{"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/posts\/710","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/comments?post=710"}],"version-history":[{"count":1,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/posts\/710\/revisions"}],"predecessor-version":[{"id":711,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/posts\/710\/revisions\/711"}],"wp:attachment":[{"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/media?parent=710"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/categories?post=710"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/molecularsciences.org\/content\/wp-json\/wp\/v2\/tags?post=710"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}echo $SHELL<\/code><\/pre>\n\n\n\nbash<\/code><\/pre>\n\n\n\ncat \/etc\/shells<\/code><\/pre>\n\n\n\nclear; echo \"This months calendar\"; cal;<\/code><\/pre>\n\n\n\nclear\necho \"This year's calendar\"\ncal -y<\/code><\/pre>\n\n\n\nchmod 755 test.sh<\/code><\/pre>\n\n\n\nbash test.sh\nsh test.sh\n.\/test.sh<\/code><\/pre>\n\n\n\nBash Variables<\/h3>\n\n\n\n
set<\/code><\/pre>\n\n\n\nnumber=10<\/code><\/pre>\n\n\n\nnumber =10\nnumber= 10\nnumber = 10<\/code><\/pre>\n\n\n\nbudget=NULL\nbudget=NULL<\/code><\/pre>\n\n\n\necho $number<\/code><\/pre>\n\n\n\nyear=\"427 BC\"\nname=Plato\ncity=Athens\necho \"$name was born in $city around $year\"<\/code><\/pre>\n\n\n\nRenaming Files in Directory<\/h3>\n\n\n\n
IMG_1232.JPG\nSP234324.JPG\nwebdown.JPG\n...<\/code><\/pre>\n\n\n\nsalzburg_1.jpg\nsalzburg_2.jpg\n...<\/code><\/pre>\n\n\n\nj=1\ns=salzburg_\nfor f in *.JPG; do\n mv $f $s$j.jpg\n j=(($j+1))\n echo renaming $f to $s$j.jpg\ndone<\/code><\/pre>\n\n\n\nSubstring<\/h3>\n\n\n\n
#!\/bin\/bash\na='Freundschaftsbezeugung'\necho $a\necho ${a:0:6} \necho ${a:6:7}\nb=${a:13:9}\necho $b<\/code><\/pre>\n\n\n\nFreundschaftsbezeugung\nFreund\nschafts\nbezeugung<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"