Tag Archives: grep

Software Development, Technology

Replace Text Recursively using grep and sed on MacOS (osX).

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As with many MacOS’isms, you have to change up your old school LINUX to work with the slightly different command syntax of the MacOS tools. Specifically in the this case xargs and sed.

xargs can be an amazingly powerful ally when automating commands line functionality, wrapping the reference command with auto-substitutions using the ‘@’ meta-character.

I’ll get to the meat of this. While trying to automated a grep -> sed pipeline, I encountered this error:

egrep -rl 'version 0.0.1' src/* | xargs -i@ sed -i 's/version 0.0.1/version 0.0.1c/g' @
xargs: illegal option -- i

It turns out that MacOS xargs like -I instead of -i.. (a quick trip to man sorted that out).

     -I replstr
             Execute utility for each input line, replacing one or more occurrences of replstr in up to replacements (or 5 if no -R flag is specified) arguments to utility
             with the entire line of input.  The resulting arguments, after replacement is done, will not be allowed to grow beyond 255 bytes; this is implemented by con-
             catenating as much of the argument containing replstr as possible, to the constructed arguments to utility, up to 255 bytes.  The 255 byte limit does not apply
             to arguments to utility which do not contain replstr, and furthermore, no replacement will be done on utility itself.  Implies -x.

Next I ran into an errors with sed.. when using the ‘edit in place’ flag -i. (yes, that makes for a confusing debug when you have the “offending” switch in two places).

egrep -rl 'version 0.0.1' src/* | xargs -I@ sed -i 's/version 0.0.1/version 0.0.1c/g' @
sed: 1: "src/com/ingeniigroup/st ...": bad flag in substitute command: 'a'
sed: 1: "src/com/ingeniigroup/st ...": bad flag in substitute command: 'a'
sed: 1: "src/com/ingeniigroup/st ...": bad flag in substitute command: 'a'
[...]

With a little testing of the individual command, and another trip to man, it took a little noodly to deduce that the error message was being generated because it was trying the sed commmand as the output file suffix and the filename as the sed command! Adding an empty string designator after sed’s -i solved this.

     -i extension
             Edit files in-place, saving backups with the specified extension.  If a zero-length extension is given, no backup will be saved.  It is not recommended to give
             a zero-length extension when in-place editing files, as you risk corruption or partial content in situations where disk space is exhausted, etc.

Final Command Query
The objective was to simply hammer through the source code and update the version tag from 0.0.1 to 0.0.1c. Running egrep in recursive filename list mode ( egrep -rl ) for the string I wanted ( ‘version 0.0.1’ ) gave me a file list, which was then piped into xargs, which expanded that list into the sed command ( sed -i ” ‘s/version 0.0.1/version 0.0.1c/g’ ). And viola.. 18 files changed with just a little big of effort: 

egrep -rl 'version 0.0.1' src/* | xargs -I@ sed -i '' 's/version 0.0.1/version 0.0.1c/g' @

Since this took me more than 5 minutes to figure out, I decided I’d take 5 more and hopefully help someone else down the line.

Software Development, Technology

Fun with ‘sed’ taking a list of table names and creating a list of T-SQL TRUNCATE commands

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Woo.. I love *NIX, especially ‘sed’ (and awk too for that matter). Wonderful things you can do to automated your programming, speed up development and really REALLY cut down on cut-paste errors.

Today’s task, was to take this list of tables… and generate a single bit fat T-SQL command to truncate them all.. *however* these tables might not exist in a given environment so each Truncate is wrapped in a test to make sure the table is there. If it’s not there, nothing to do, not to mention avoid a potential fatal error trying to truncate a non-existent table.

Here is a snippet of the tables in question:

…
FCT_CRIMINOGENIC_NEED_TOP_DOMAINS
FCT_DETENTION_RISK_RESPONSE_DETAILS
FCT_DETENTION_RISK_RESPONSE_FULL
…

This is the desired T-SQL for these three tables

— Truncate table FCT_CRIMINOGENIC_NEED_TOP_DOMAINS
IF EXISTS (SELECT * FROM sys.objects WHERE NAME = ‘FCT_CRIMINOGENIC_NEED_TOP_DOMAINS’)
BEGIN
TRUNCATE TABLE FCT_CRIMINOGENIC_NEED_TOP_DOMAINS
END

— Truncate table FCT_DETENTION_RISK_RESPONSE_DETAILS
IF EXISTS (SELECT * FROM sys.objects WHERE NAME = ‘FCT_DETENTION_RISK_RESPONSE_DETAILS’)
BEGIN
TRUNCATE TABLE FCT_DETENTION_RISK_RESPONSE_DETAILS
END

— Truncate table FCT_DETENTION_RISK_RESPONSE_FULL
IF EXISTS (SELECT * FROM sys.objects WHERE NAME = ‘FCT_DETENTION_RISK_RESPONSE_FULL’)
BEGIN
TRUNCATE TABLE FCT_DETENTION_RISK_RESPONSE_FULL
END

The Sed Command

sed ‘s#^\(.*\)#– Truncate table \1 \’$’\nIF EXISTS (SELECT * FROM sys.objects WHERE NAME = \’\\1\’) \\’$’\n BEGIN \\’$’\n TRUNCATE TABLE \\1 \\’$’\nEND \\’$’\n#g’ MY_INPUT_FILE

Secret Sauce Ingredients

Setting up the string match. In this case it was simple.. I wanted the entire line which is represented with .*

\(.*\)

This loads the matching string into an internal register in ‘sed’ that can be references as ‘1’ within the output replacement expression. This is what it looks like in the command:

\1

Adding a newline in the output.. this was the big trick, and requires dropping into the shell to generate the desired output. The string in the command looks like this:

\’$’\n

You may notice after the first drop into the shell, the escaping has to be doubled for the substitution and the newline…

\\1 \\’$’\n

I cannot speak to the reason for this, but that is what I encountered and why the substitutions change in the latter part of the string. You may find that is not necessary, or might cause an issue in your environment. Adjust as necessary.