Tag Archives: efficient

Faster Vim search/replace

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Entering search patterns and replacement strings in Vim can sometimes be a pain, particularly if the search or replacement text is already available in a register or under the cursor. There are a few ways to make working with search and replace in Vim quicker and less cumbersome for some common operations, and thereby save a bit of error-prone typing.

Insert contents of a register

As in command mode or insert mode, you can insert the contents of any register by pressing Ctrl+R and then the register key. For example, to directly insert the contents of register a, you can type Ctrl+R and then a while typing a search pattern or replacement string.

Reference contents of a register

Similarly, if you want to use the contents of a register in a pattern or replacement but don’t want to directly insert it, you can instead reference the contents of register a with \=@a:

:s/search/\=@a/

Both of the above tips work for both the search and replacement patterns, and for special registers like " (default unnamed register) and / (last searched text) as well as the alphabetical ones.

Insert word under cursor

If you happen to be hovering over a word that you want to use as as a search or replacement string, as a special case of the above you can do so by typing Ctrl+R and then Ctrl+W for a normal word, or Ctrl+R and then Ctrl+A for a space-delimited word.

Empty search string

You can use the previous search as a search pattern or replacement string by including it from the special / register, in the same way as any other register above, by inserting it with Ctrl+R and then /, or representing it with \=@/. There’s a convenient shorthand for this however in just using an empty search string:

:s//replacement/

This will replace all occurences of the previous search string with replacement. It turns out to be a particularly convenient shorthand when searching for words by pressing * or #.

Elegant Awk usage

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For many system administrators, Awk is used only as a way to print specific columns of data from programs that generate columnar output, such as netstat or ps. For example, to get a list of all the IP addresses and ports with open TCP connections on a machine, one might run the following:

# netstat -ant | awk '{print $5}'

This works pretty well, but among the data you actually wanted it also includes the fifth word of the opening explanatory note, and the heading of the fifth column:

and
Address
0.0.0.0:*
205.188.17.70:443
172.20.0.236:5222
72.14.203.125:5222

There are varying ways to deal with this.

Matching patterns

One common way is to pipe the output further through a call to grep, perhaps to only include results with at least one number:

# netstat -ant | awk '{print $5}' | grep '[0-9]'

In this case, it’s instructive to use the awk call a bit more intelligently by setting a regular expression which the applicable line must match in order for that field to be printed, with the standard / characters as delimiters. This eliminates the need for the call to grep:

# netstat -ant | awk '/[0-9]/ {print $5}'

We can further refine this by ensuring that the regular expression should only match data in the fifth column of the output, using the ~ operator:

# netstat -ant | awk '$5 ~ /[0-9]/ {print $5}'

Skipping lines

Another approach you could take to strip the headers out might be to use sed to skip the first two lines of the output:

# netstat -ant | awk '{print $5}' | sed 1,2d

However, this can also be incorporated into the awk call, using the NR variable and making it part of a conditional checking the line number is greater than two:

# netstat -ant | awk 'NR>2 {print $5}'

Combining and excluding patterns

Another common idiom on systems that don’t have the special pgrep command is to filter ps output for a string, but exclude the grep process itself from the output with grep -v grep:

# ps -ef | grep apache | grep -v grep | awk '{print $2}'

If you’re using Awk to get columnar data from the output, in this case the second column containing the process ID, both calls to grep can instead be incorporated into the awk call:

# ps -ef | awk '/apache/ && !/awk/ {print $2}'

Again, this can be further refined if necessary to ensure you’re only matching the expressions against the command name by specifying the field number for each comparison:

# ps -ef | awk '$8 ~ /apache/ && $8 !~ /awk/ {print $2}'

If you’re used to using Awk purely as a column filter, the above might help to increase its utility for you and allow you to write shorter and more efficient command lines. The Awk Primer on Wikibooks is a really good reference for using Awk to its fullest for the sorts of tasks for which it’s especially well-suited.