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By converting a variable into the standard input stream we were able to pass it to grep.
#Ksh grep output file how to
In this Linux quick tip we demonstrated how to grep a string from a variable. When using Linux there are always several ways to accomplish a task.
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To do this, you must first tell grep to only show the matching characters with the -o (-only-matching) option. You can use the wc utility to count the number of times a string is found in a variable. Counting the Instances of a String in a Variable Using the here string allows you to easily grep a string from a variable. To use a here string, simple add three less than symbols in front of the variable name like so: It basically allows you to feed a variable to a command as standard input (STDIN). Using a Here StringĪ here string is a stripped down version of a here document. To learn more about standard streams (STDIN, STDOUT, & STDERR) and Pipelines, read " Linux I/O, Standard Streams and Redirection". It's is not the most graceful solution, but it works. This allows us to use grep to match a pattern from a variable. If we send the output of echo into a pipeline, grep will receive it on the other side as standard input (STDIN). We can turn the variable into standard output (STDOUT) using the echo command. There are multiple ways we can accomplish this. it returns all lines of the file given by filename that matches string foo. It seems we need to pass the variable as standard input to grep. The grep (Global Regular Expression Print) is a unix command utility that. Here is a demonstration of grep accepting standard input and matching the letter "a". Grep searches the named input FILEs (or standard input if no files are named) for lines containing a match to the given PATTERN. Well, we know that grep accepts standard input.
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So the question is, how can we get around this? When expanded, grep recognizes it as multiple arguments where a filename should be. This happens because the variable is expanded by the shell. Grep: variable: No such file or directory Search and display the total number of times that the string ‘nixcraft’ appears in a file named frontpage.md: grep -c 'nixcraft' frontpage.md. ~]$ I="This is a variable set on the command line" Look for all files in the current directory and in all of its subdirectories in Linux for the word ‘httpd’: grep -R 'httpd'. But, what if you want to grep a string in a variable? If you pass a variable as an argument to grep, you will get an error (or several if your variable contains spaces). Most people are familiar with using grep to print lines that match a string from a file.