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Wednesday, December 17, 2008

Command-line automation – find and findstr

This is the second in a series of posts containing information on what I consider the building blocks to automate repetitive tasks at the Windows command-line. These components are the for, find, findstr, set, if and echo commands, control files used to control data input, combined with errorlevels, command concatenation, nested loops and if/then/else constructs.

Described in this post are the ‘find’ and ‘findstr’ commands - unless you want to spend all your time manually creating or filtering control files you will often use these commands when constructing repeatable command-lines.

These two commands are crucial in efficient ‘for’ loop processing, invaluable when filtering a control file or the results of an in-line command. Help on each is available from the command prompt with the ‘/?’ argument.

Find

I usually use find because more often than not I want to filter a string literal – a specific word or combination of characters – from an input string. As often as not, I also use ‘find /v’, returning the lines that don’t match the specified string.

For example, if you have a control file listing servers in several geographic locations, but you are only interested in processing servers in ‘bne’ (case insensitive with ‘/i’), you could run:
find /i "bne" c:\temp\control.txt

Combined with a ‘for’ command, this could be:
for /f "skip=2" %i in ('find /i "bne" c:\temp\control.txt') do echo %i

Note that this line uses the following syntax explained in the previous post on ‘for’:

  1. ‘Skip=2’ tells the loop to skip the first two lines – the result header of the ‘find’ command
  2. Inside the brackets I’ve specified to run a command and parse the results, wrapping the command in single-quotes.

The results are that for each server containing the word ‘bne’, the body of the ‘for’ statement will be executed – in this case simply to echo the first token.

You might also want to run the commands against all servers except those in bne, which is the above command repeated with the addition of the ‘/v’ switch to tell ‘find’ to return those lines not containing a match:
for /f "skip=1" %i in ('find /i /v "bne" c:\temp\control.txt') do echo %i

Filtering in-line output with find

Filtering output of a command executed within a ‘for’ loop is syntactically a little more complicated, but makes sense once you get the hang of it. For example, suppose you want to filter the output of a ping command, returning the IP address of those hosts that replied to a ping, you could run:
for /f "tokens=3" %i in ('"ping -n 1 computer find /i "reply""') do @echo %i

This will:

  • Execute the ping command, pinging the host named computer, filtering the output to find the word ‘reply’ (indicating a successful reply). Note that to use the pipe inside the brackets, the whole string needs to be enclosed in double-quotes – inside the single-quotes.
  • Using spaces/tabs, choose the third token to return in the first variable - %i. This will be the IP address in the standard ping output returned by XP and Vista.

Unfortunately the third token of the ping output includes a irrelevant colon, so to strip that, we could specify colons and spaces as delimiters in the for loop:
for /f "tokens=3 delims=: " %i in ('"ping -n 1 computer find /i "reply""') do echo %i

This will be better explained in a future post, but you can also nest two ‘for’ commands and for each host in the control file (in bne in this example), ping and return the IP address if there is a reply:
for /f "skip=2" %i in ('find /i "bne" c:\temp\control.txt') do @for /f "tokens=3 delims=: " %m in ('"ping -n 1 %i find /i "reply""') do @echo %i,%m

The output would give you a comma-separated list of server names and IP address of those from the original control file that currently respond to a ping. Theoretically not all that useful with servers, as they’d usually be known IPs and always on, but if you’re wanting to check something on hundreds or thousands of workstations this would give you a point-in-time control file of online machines (assuming name resolution is accurate).

It’s also worth noting that ‘find’ commands can be cascaded – piping the output of one find command to another if you need to further refine the output. For example to find servers in ‘bne’ and then servers in ‘bne’ that also contain ‘vm’:
find /i /c "bne" c:\temp\control.txt find /i "vm"

The possibilities are nearly endless, I use ‘find’ to:

  • Filter in and out items that I want, ‘find /i’ and ‘find /i /v’ from generic control files that I use for multiple operations, either in-line in a for command, or to create a stand-alone filtered control file
  • Run commands and then filter out useless or useful information, often headers/footers or other extraneous detail, making it possible to list data, filter that data and run a command against each filtered item in a single command.
  • Use errorlevels to determine whether the find command was successful or not (explained in a future post). Often the only way of knowing whether a command returned what you were after is the presence or absence of a string – and ‘find’ will tell you this based on the errorlevel (an advantage over findstr which in XP at least does not set the errorlevel).

Note that find also has several other features that are useful in some scenarios:

  • By default, offline files will be skipped – if you use a file archiving product that sets the offline (‘O’) attribute, these files will not be searched unless you specify the /offline parameter
  • The ‘find /n’ option will return the line number the match was found, occasionally useful when parsing large or sequenced control files and you want to know where in a file the string was found.
  • The ‘find /c’ option will return a count of the matches found, instead of the actual matching lines. This can often be useful when determining how many records would be processed. For example, in the example above you could first run the following command to determine how many records would be processed with the for loop:
    find /i /c "bne" c:\temp\control.txt

Findstr

These same principles can be used with findstr to filter output – findstr provides advanced searching, with the following benefits in my use of the commands, you can:

  • Search for more than one string in a single command. This simplifies searches, in the example above, you could search for ‘bne’ and ‘syd’ in a single findstr command.
  • Use basic regular expressions and/or string literals

In the example above with a control file containing a list of servers with geographic names (or descriptions somewhere on the line), you could run the following command to return servers in both syd and bne and then run the subsequent command against each server:
for /f %i in ('findstr /i /c:bne /c:syd c:\temp\control.txt') do echo %i

Regular expressions are used to group similar items, without expressly providing each possible combination. For example, parsing robocopy log output, to search for new directories that have been created with a regular expression, you could run:
findstr /i /n "^.*New.Dir" Robocopy.log"

You could just use ‘find’ and search for the string ‘new dir’, but this could easily return false positives if a file or directory has the string ‘new dir’ in it. Using the regular expression looking for the start of the line followed by whitespace followed by the ‘New Dir’ is much more precise.

This was a basic overview of the ‘find’ and ‘findstr’ commands, future posts will build on this foundation with other useful commands, error levels, if/then/else statements and nested ‘for’ loops.

For more real-world examples of how I use the ‘find’ and ‘findstr’ commands, see my command-line operations:
http://waynes-world-it.blogspot.com/2008/09/useful-ntfs-and-security-command-line.html
http://waynes-world-it.blogspot.com/2008/09/useful-windows-printer-command-line.html
http://waynes-world-it.blogspot.com/2008/09/useful-windows-mscs-cluster-command.html
http://waynes-world-it.blogspot.com/2008/09/useful-vmware-esx-and-vc-command-line.html
http://waynes-world-it.blogspot.com/2008/09/useful-general-command-line-operations.html
http://waynes-world-it.blogspot.com/2008/09/useful-dns-dhcp-and-wins-command-line.html
http://waynes-world-it.blogspot.com/2008/09/useful-active-directory-command-line.html


Wayne's World of IT (WWoIT), Copyright 2008 Wayne Martin.

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About Me

I’ve worked in IT for over 13 years, and I know just about enough to realise that I don’t know very much.