Linux Commands You’ve Never Used

Technology

# lsof | grep TCP
portmap    2587   rpc  4u   IPv4     5544  TCP *:sunrpc (LISTEN)
rpc.statd  2606  root  6u   IPv4     5585  TCP *:668 (LISTEN)
sshd       2788  root  3u   IPv6     5991  TCP *:ssh (LISTEN)
sendmail   2843  root  4u   IPv4     6160  TCP badhd:smtp (LISTEN)
vsftpd     9337  root  3u   IPv4    34949  TCP *:ftp (LISTEN)
cupsd     16459  root  0u   IPv4    41061  TCP badhd:ipp (LISTEN)

Here’s a short list of useful Linux shell programs, many of which you may have never known about. I’ve got a new favorite shell command, lsof (shown above), which displays information on every open file handle. – Link.

If I could add one to the list, it’d have to be the short and sweet command line search and replace using perl:

perl -pi -e 's/searchpattern/replacewith/g' *.html

Do you have a favorite command line secret? Please share it in the comments.

12 thoughts on “Linux Commands You’ve Never Used

  1. A.Nonny.Mouse says:

    This is probably a well known trick, but I like xargs.
    It takes standard in and treats it as an argument to a command give in the args of xargs… So, for example, say you have a web directory tree with a mixed bag of php, html, css and xml files. If you only want to search for something in the php files you can do this:

    find . -name “*.php” | xargs grep -i “special”

    That’ll find only the php files and grep them for special.

    You could also pipe ps through awk and use xargs to kill all of a certain process…

    But everybody probably already knew that.

  2. jher says:

    can’t get something to unmount so you can restart autofs?

    try this:

    ps -ef |grep rpciod |awk ‘{print $2}’ |xargs kill -9

    This doesn’t actually cause rpciod to die, it just forces it to release any stuck nfs mount points (in linux).

  3. illovich says:

    For the record (or for the mac users, I guess) I thought I would point out that the following from the page 10 linux commands also work in the Mac OS X terminal:

    #3 bc
    #4 split
    #5 nl
    #6 mkfifo
    #8 col
    and
    #10 lsof

    Additionally xargs is available as well (from the first tip).

  4. LBonanomi says:

    I’m begging you, please don’t pipe grep out to awk. Awk can match patterns all by it’s lonesome. In fact, if you find awk in a pipeline with cat, grep, tr, wc or sed you need to stop and re-think whats happening.

    Awk handles files without a cat pipeline. Awk can make its own text substitutions with sub and gsub. Awk can count lines with ‘END { print NR }’. If your version of awk doesn’t accept environment variables (my old rationale for using grep | awk…) use:
    eval awk ‘/$1/ { print }’

    Awk may not have the horsepower of perl, but it can do a lot more than act as a heavier version of cut.

  5. ctb says:

    I always enjoy passing multiple files or directories with curly brackets. This is nice for changing permissions on a handful of items really quickly, i.e…

    chmod 755 {file1,file2,dir1,file3}

    Or for creating a handful of directories in one swipe…

    mkdir {music,images,text,archive}

  6. MCasillo says:

    A.Nonny.Mouse – this will also work for your example :)
    grep -i “special” *.html

    Another neat shell trick for commands without an ‘ignore case’ command is to use bracketed ‘sets’ :

    chmod all .Zip or .zip files
    chmod 755 help.[Zz]ip

    chmod all files named help.zip (or HelP.zIP, etc)
    chmod 755 [Hh][Ee][Ll][Pp].[Zz][Ii][Pp]

    chmod all files that start with the letter ‘s’ but do not end in any form of zip:

    chmod 755 [Ss]*.[!Zz][!Ii][!Pp]

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