{"id":1060,"date":"2008-04-02T18:46:00","date_gmt":"2008-04-02T18:46:00","guid":{"rendered":"https:\/\/isplotchy.com\/blog\/?p=1060"},"modified":"2013-05-04T01:42:24","modified_gmt":"2013-05-04T01:42:24","slug":"unix-script-goodness-and-variable-prefixsuffix-stripping-fun","status":"publish","type":"post","link":"https:\/\/isplotchy.com\/blog\/2008\/04\/unix-script-goodness-and-variable-prefixsuffix-stripping-fun\/","title":{"rendered":"UNIX Script Goodness And Variable Prefix\/Suffix Stripping Fun"},"content":{"rendered":"

\"\"<\/a>
Here’s something you probably have no interest in, but it’s a script I wrote to help me with UNIX shell programming that I engage in from time to time.<\/p>\n

There’s a nice way of easily taking a piece of text (often called a “String” by programmer-types) and stripping off pieces of it, either from the front or the back, using variable evaluation.<\/p>\n

One thing to note about UNIX is that are many, many different ways to do the same thing. This is just one little feature of UNIX I like to use.<\/p>\n

I wrote a script to help me when I want to do this prefix\/suffix stripping kind of variable evaluation.<\/p>\n

Here is the script in its entirety:<\/p>\n

function showUsage {
print
print ‘USAGE:’
print ‘ksh -f variableTest.sh ‘
print
print ‘=============================================================================================================’
print ‘${variable#pattern} evaluates variable, but removes the smallest portion of its prefix which matches pattern.’
print ‘${variable##pattern} evaluates variable, but removes the largest portion of its prefix which matches pattern.’
print ‘${variable%pattern} evaluates variable, but removes the smallest portion of its suffix which matches pattern.’
print ‘${variable%%pattern} evaluates variable, but removes the largest portion of its suffix which matches pattern.’
print ‘=============================================================================================================’
print
print ‘Special instructions:’
print ‘======================’
print ‘To stop the shell from interpreting wildcards you may use for patterns,’
print ‘run this script like the following:’
print
print ‘ksh -f variableTest.sh ‘
print
print EXAMPLE: ksh -f variableTest.sh aabbcc \\’a*\\’
print
print
exit 1
}<\/p>\n

clear<\/p>\n

if [ $# -ne 2 ]
then
showUsage
fi<\/p>\n

variable=$1
pattern=$2<\/p>\n

print
print ‘=============================================================================================================’
print ‘${variable#pattern} evaluates variable, but removes the smallest portion of its prefix which matches pattern.’
print ‘${variable##pattern} evaluates variable, but removes the largest portion of its prefix which matches pattern.’
print ‘${variable%pattern} evaluates variable, but removes the smallest portion of its suffix which matches pattern.’
print ‘${variable%%pattern} evaluates variable, but removes the largest portion of its suffix which matches pattern.’
print ‘=============================================================================================================’
print
print ‘variable: ‘ $variable
print ‘pattern: ‘ $pattern
print
print ‘${variable#pattern} ‘ ${variable#$pattern}
print ‘${variable##pattern} ‘ ${variable##$pattern}
print ‘${variable%pattern} ‘ ${variable%$pattern}
print ‘${variable%%pattern} ‘ ${variable%%$pattern}<\/pattern><\/string><\/pattern><\/string><\/span><\/p>\n

Most of this script is just printing stuff out to the screen. There’s a whole big piece of code that just tells you how to run the script.<\/p>\n

Anyways, say you want to find out what directory you are in on a UNIX file system, and want to save this off in a variable, but without all the nested subdirectories your directory rests in (UNIX is all about the nested subdirectories).<\/p>\n

You can use this script to figure out the right pattern to get your current directory minus the path.<\/p>\n

Example:<\/span><\/p>\n

Let’s say I’m in:
\/usr\/appl\/abc\/very\/very\/long\/directory<\/span><\/p>\n

After some trial and error running my script, I can eventually figure out how to get my current directory, minus the path.<\/p>\n


>ksh -f variableTest.sh \/usr\/appl\/abc\/very\/very\/long\/directory ‘*\/’<\/p>\n

variable: \/usr\/appl\/abc\/very\/very\/long\/directory
pattern: *\/<\/p>\n

${variable#pattern} usr\/appl\/abc\/very\/very\/long\/directory
${variable##pattern} directory
${variable%pattern} \/usr\/appl\/abc\/very\/very\/long\/directory
${variable%%pattern} \/usr\/appl\/abc\/very\/very\/long\/directory
<\/span><\/p>\n

Your current working directory (including the path) is stored in a variable called $PWD.<\/p>\n

So, to get your current working directory only in a script you are writing, you can just write the following line:<\/p>\n


MY_DIRECTORY=${PWD##*\/}
<\/span><\/p>\n

Why did I write a script to do this? Because I can never<\/span> remember how the pattern matching works, and thought it would be easier to write a script to show me instead.<\/p>\n

Now, you’re probably asking me, “Splotchy, why would you put something in a program that many, including you, do not fully understand or remember how it works?”<\/p>\n

As Matty Boy<\/a> would say, that’s a great question, hypothetical question asker<\/span>!<\/p>\n

One thing that I neglected to mention about UNIX programming is that it is notoriously squirrelly. And this feature I am making use of is pretty damned squirrelly, too.<\/p>\n","protected":false},"excerpt":{"rendered":"

Here’s something you probably have no interest in, but it’s a script I wrote to help me with UNIX shell programming that I engage in from time to time. There’s a nice way of easily taking a piece of text (often called a “String” by programmer-types) and stripping off pieces of it, either from the … Continue reading UNIX Script Goodness And Variable Prefix\/Suffix Stripping Fun<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"episode_type":"","audio_file":"","podmotor_file_id":"","podmotor_episode_id":"","cover_image":"","cover_image_id":"","duration":"","filesize":"","filesize_raw":"","date_recorded":"","explicit":"","block":"","jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[14,55,218],"tags":[],"class_list":["post-1060","post","type-post","status-publish","format-standard","hentry","category-computers","category-geek","category-unix"],"yoast_head":"\nUNIX Script Goodness And Variable Prefix\/Suffix Stripping Fun - SPLOTCHY<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/isplotchy.com\/blog\/2008\/04\/unix-script-goodness-and-variable-prefixsuffix-stripping-fun\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"UNIX Script Goodness And Variable Prefix\/Suffix Stripping Fun - SPLOTCHY\" \/>\n<meta property=\"og:description\" content=\"Here’s something you probably have no interest in, but it’s a script I wrote to help me with UNIX shell programming that I engage in from time to time. 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