Command line not recognizing metacharacters in awk
Hello, I'm new to command line coding (and coding in general) and have run into a problem. I'm using awk to perform a global find and replace in a text file in the Terminal provided by Mac.
Here is a sample of my textfile where the fields are separated by tabs.
Code:
1Ps 1,1 VWB/(J VWB VWB
2 Ps 1,1 &WHJ== WHJ HJ==
3 Ps 1,1 L L L
4 Ps 1,1 GBR/~> GBR> GBR
5 Ps 1,1 D D D
I want to add a space after the digit that is preceded by a comma (this is because my columns become upset when there is a two-digit number after the coma in other parts of my data). To do this, I used the following:
Code:
awk '{gsub(",[0-9]",",[0-9] "); print}' textfile
However, I got the following output whereby the character class '[0-9]' was not recognized.
Code:
1 Ps 1,[0-9] VWB/(J VWB VWB
2 Ps 1,[0-9] &WHJ== WHJ HJ==
3 Ps 1,[0-9] L L L
4 Ps 1,[0-9] GBR/~> GBR> GBR
5 Ps 1,[0-9] D D D
Can someone please tell me what I'm going wrong and how to set up my code and/or Terminal to recognize regex metacharacters?
Moderator's Comments:
Unfortunately, the sample data that you posted here contains spaces instead of tabs.
Last edited by jvoot; 08-13-2014 at 08:55 PM..
Reason: Add CODE tags.
Thanks so much for this pilnet101. Actually, I'm trying to get the space *after* the digit which follows the comma, that is to say, a space before the tab that delimits the field.
Ultimately, I'd like each record of the textfile to look like this:
Code:
1 Ps 1,1[space][tab] VWB/(J ...
I'm trying to add that [space] above to accommodate a future double digit, i.e.,
Code:
Ps 1,10[Tab]Field $2
So, I'm trying to add a single space when there is only one digit after the comma (,1 ) and not have that space when there are two digits after the comma (,11).
Thanks so much and I apologize for my inability to explain this sufficiently. I am very new to this.
if you only want to change one occurrence of something, use sub() instead of gsub(), and
the problem you're seeing isn't the ERE, the real problem is the replacement string you're using. The [0-9] in the replacement string is literal text; not an RE. In the replacement text, an unescaped ampersand (&) is replace by the string that was matched by the RE.
pilnet101 already showed you how to do this with sed, but if you're doing other stuff to your file in awk (that you haven't shown us), there is no reason to use both sed and awk. So, if you want to do it in awk try changing:
Code:
gsub(",[0-9]",",[0-9] ")
to:
Code:
sub(",[0-9]","& ")
The & would also simplify the sed command. Some versions of awk will allow you to use the backreferences pilnet101 used in sed in sub() calls in awk, but that is a non-standard extension that is not always available. (The awk utility uses extended regular expressions while the sed utility uses basic regular expressions.
If you have tabs in your input file as field separators and want to add a space before an existing tab in your input and preserve other tabs in your input, change your script to:
Don, just one thing regarding your post - you would require a space after [0-9] expression as per OP's requirement to "not have that space when there are two digits after the comma".
That's right pilnet101. This resulted in a space after every digit that followed the comma, rather than just when there is one digit.
I really really appreciate the help pilnet101 and Don!
Quote:
Originally Posted by pilnet101
Don, just one thing regarding your post - you would require a space after [0-9] expression as per OP's requirement to "not have that space when there are two digits after the comma".
As per requirement if column 2 is NULL then 'N' ELSE 'Y'.
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cat temp.txt
1|abc|3
1||4
1|11|c
awk -F'|' '{if($2==""){$2="N"}else{$2="Y"} print $0 } {OFS="|"} ' < temp.txt
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08-13-2014
