{"id":3446,"date":"2014-11-11T14:10:15","date_gmt":"2014-11-11T14:10:15","guid":{"rendered":"https:\/\/www.inmotionhosting.com\/support\/2014\/11\/11\/sed\/"},"modified":"2014-11-11T14:10:15","modified_gmt":"2014-11-11T14:10:15","slug":"sed","status":"publish","type":"post","link":"https:\/\/www.inmotionhosting.com\/support\/server\/linux\/sed\/","title":{"rendered":"sed command"},"content":{"rendered":"
\n

In this tutorial:<\/h2>\n

Command structure<\/a> Commands<\/a> Examples<\/a> <\/div>\n

Sed<\/em> (short for ‘s<\/strong>tream’ ‘ed<\/strong>itor’ is a special editor that is used for modifying files automatically. It is not an interactive editor, so it can be used if you are wanting to write a program to make changes in a file. Follow along below as we go through several examples of the sed<\/em> command.<\/p>\n

<\/a> <\/p>\n

Command Structure<\/h2>\n

Command: <\/strong>sed
Synopsis: <\/strong>sed [OPTION]… {script-only-if-there-is-no-other-script} [input-file]…<\/p>\n

List of Options: <\/strong> <\/p>\n

NOTE:<\/strong> Some options have only a short name, some only a long name, and some both. If an option has both, then you may use either format. <\/div>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Short Name<\/th>\nLong name<\/th>\nDescription<\/th>\n<\/tr>\n
-n<\/td>\n–quiet –silent<\/td>\nThis is quiet mode, where it does not print out anything unless a specific print request exists.<\/td>\n<\/tr>\n
-e script<\/td>\n–expression=script<\/td>\nAdd the script to the commands to be executed.<\/td>\n<\/tr>\n
-f script-file<\/em><\/td>\n–file=script-file<\/em><\/td>\nThis adds the contents of the ‘script-file’ to the commands to be executed<\/td>\n<\/tr>\n
<\/td>\n–follow-symlinks<\/td>\nFollows symlinks when processing. The hard links will still be broken.<\/td>\n<\/tr>\n
-i[SUFFIX]<\/td>\n–in-place[=SUFFIX]<\/td>\nThis will edit the files in place and make backups if an extension is supplied.<\/td>\n<\/tr>\n
-c<\/td>\n–copy<\/td>\nThis is used when shuffling files using the -i<\/em> option. It avoids breaking links, both hard and symlinks. –follow-symlinks<\/em> is usually a better option, however, as it is both more secure and faster.<\/td>\n<\/tr>\n
-l N<\/td>\n–line-length=N<\/td>\nUse this command to specify thelength of a line, N, before it wraps.<\/td>\n<\/tr>\n
<\/td>\n–posix<\/td>\nTHis disables al the GNU extensions.<\/td>\n<\/tr>\n
-r<\/td>\n–regexp-extended<\/td>\nCommand to use extended regular expressions in the script.<\/td>\n<\/tr>\n
-s<\/td>\n–separate<\/td>\nConsider each file separately as opposed to one long stream.<\/td>\n<\/tr>\n
-u<\/td>\n–unbuffered<\/td>\nLoad minimal amounts of data form the input files and flus the output buffers more often.<\/td>\n<\/tr>\n
<\/td>\n–version<\/td>\nPrints out the version information<\/td>\n<\/tr>\n<\/table>\n

<\/a> <\/p>\n

List of Commands<\/h2>\n\n\n\n\n\n\n\n
Structure<\/th>\nDescription<\/th>\n<\/tr>\n
=<\/td>\nUsed to print line numbers where the supplied parameter is found.<\/td>\n<\/tr>\n
a \\text<\/em><\/td>\nAppend text. This command inserts a new line and any specified text AFTER the specified parameter.<\/td>\n<\/tr>\n
c \\text<\/em><\/td>\nThis command is used to find the line the specified parameter is on and then change it to the text provided.<\/td>\n<\/tr>\n
i \\text<\/em><\/td>\nInsert text. This command inserts a new line and any specified text BEFORE the specified parameter.<\/td>\n<\/tr>\n
s \/regexp\/replacement<\/td>\nThis looks through the file looking to match the regexp<\/em> parameter. Once found, it replaces it with the replacement<\/em> parameter.<\/td>\n<\/tr>\n<\/table>\n

<\/a> <\/p>\n

Examples<\/h2>\n

Using the commands and options above, you can create many different combinations to tailor sed<\/em> to filter your files. Below are several examples using the command and options.<\/p>\n

Substitution with sed s<\/h3>\n

This is one of the most often used options. This example below uses sed<\/em> to look through a file named old.txt<\/em> and substitute the word ‘day’ for ‘night’, saving the result to a file named ‘new.txt.’ <\/p>\n

 # sed 's\/day\/night\/' old.txt > new.txt<\/span> <\/pre>\n
When we cat<\/em> the original ‘old.txt’ file, you can see it has two words.<\/p>\n
 # cat old.txt<\/span> day night <\/pre>\n
After running our command, when we cat<\/em> the ‘new.txt’ file, you can see the word ‘day’ has been replaced with ‘night’.<\/p>\n
 # cat new.txt<\/span> night night <\/pre>\n<\/p>\n
Changing the delimiter for the s command<\/h3>\n
When using the s<\/em> command in the example above, we preceded the parameters with a forward slash \/. This works fine in many cases, but if you are wanting to use filepaths in your parameters, you may want to choose a different delimiter. To do this, simply precede the first parameter with your chosen parameter. For example, below we want to change the apth \/home\/userna5\/public_html<\/em> to \/home\/userna5\/public_html\/testfolder<\/em>.<\/p>\n
You could still use the slash delimiter, but you would need to escape all the slashes in your path, so it would end up looking like this:  <\/p>\n
 # sed '\/\\\/home\\\/userna5\\\/public_html\/\\\/home\\\/userna5\\\/public_html\\\/testfolder\/' old.txt > new.txt<\/span> <\/pre>\n
 This is quite ugly and can be confusing when trying to read it. <\/p>\n
Now, by using a different delimiter, it is much easier to read. Below we display delimiters using a colon : and a pipe |. These are also commonly used delimiters.  <\/p>\n
 # sed ':\/home\/userna5\/public_html:\/home\/userna5\/public_html\/testfolder:' old.txt > new.txt<\/span> <\/pre>\n
 # sed '|\/home\/userna5\/public_html|\/home\/userna5\/public_html\/testfolder|' old.txt > new.txt<\/span> <\/pre>\n<\/p>\n
Adding a line with the a command<\/h3>\n
If you want to insert some information on a new line, you can do so with the ‘a<\/em>‘ command. Here we want to add a new line with the sentence ‘This is new’ after the word ‘day’ from the ‘old.txt’ file and save it as ‘new.txt.’<\/p>\n
 # sed '\/day\/ a\\This is new' old.txt > new.txt<\/span> <\/pre>\n
 When we nano the ‘new.txt’ file, we see the newly added content was inserted correctly. <\/p>\n
 # cat new.txt<\/span> day This is new night <\/pre>\n
Changing a line with the c command<\/h3>\n
Rather than inserting a line, you can also change an existing line using the c<\/em> command. In the example below, we use sed<\/em> to change a line with the number 2 in it to say ‘ne new new!’. You do need to be careful because as you notice, it also changed the lines numbered 12 and 20 because they also had a 2 in them. Sed<\/em> can be pretty greedy and make changes whenever possible, so be as accurate as you can when specifying what to change.<\/p>\n
 # sed '\/2\/ c\\new new new!' old.txt > new.txt<\/span> <\/pre>\n
 # cat new.txt<\/span> 1 day new new new! 3 4 5 6 7 8 9 10 11 new new new! 13 14 15 16 17 18 19 new new new! <\/pre>\n
Finding the line number for a parameter using =<\/h3>\n
You can use sed<\/em> to find the line number for a given parameter. For example, if I want to search a file named ‘new.txt’ for the word ‘new’, it would return a list of line numbers that contain that word. In the example below, we also use the option -n<\/em> so that it only prints out the line numbers involved. <\/p>\n
 # sed -n '\/new\/ =' new.txt<\/span> 2 12 20 <\/pre>\n
 As you can see, the word new was found on lines 2, 12, and 20. <\/p>\n","protected":false},"excerpt":{"rendered":"
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