Replace string in text file using Bash

Question

I have some really simple questions which have bothered me all day:

How can I get the first number in $variable?
How can I remove the first number before ";"?
How can I change the number with $updateNum?

$updateNum= 1

$variable="2;,A1,A2,A3,A4,A5,A6,A7,B1,B2,B3,B4,B5,B6,B7,C1,C2,C3,C4,C5,C6,C7,D1,D2,D3,D4,D5,D6,D7,E1,E2,E3,E4,E5,E6,E7,F1,F2,F3,F4,F5,F6,F7,G1,G2,G3,G4,G5"`

mpapis · Accepted Answer · 2012-11-23 13:39:24Z

2

try:

oldVal="${variable%%;*}"
variable="$updateNum;${variable#*;}"

answered Nov 23, 2012 at 13:39

mpapis

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1 Comment

Shahbaz Over a year ago

This website would help: cyberciti.biz/tips/bash-shell-parameter-substitution-2.html

Chris Seymour · Accepted Answer · 2012-11-23 22:03:28Z

0

This will do it all in one go:

variable=$(echo $variable | sed -E "s/[0-9]+?/$updateNum/")

Benchmark:

time variable=$(echo $variable | sed -E "s/[0-9]+?/$updateNum/") 

real    0m0.002s
user    0m0.001s
sys     0m0.000s

edited Nov 23, 2012 at 22:03

answered Nov 23, 2012 at 14:45

Chris Seymour

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5 Comments

mpapis Over a year ago

using subprocesses slows down the execution, on one call - no big difference, on 20 calls you get into secconds

Chris Seymour Over a year ago

That is not a reason to downvote!? This solution for the given problem size is clear and easy to understand. Adding a comment to say 'doesn't scale well' is helpful but downvotes are for wrong answer, which this is not.

mpapis Over a year ago

I do a lot shell scripting, and this is just a bad practice for me - counts for a downvote, this solution should be avoided unless you can justify it - which I can not.

Chris Seymour Over a year ago

To a beginner your solution looks very confusing i'm sure and you have offered no explanation (neither have I but i'm not the one downvoting) also alinsoar solution is an incomplete mess but you didn't downvote his? Are you sure the unjust downvote has nothing to do with the fact the OP accepted my answer?

mpapis Over a year ago

sorry it has nothing to do with the fact of accepted answer, it's just a bad practice and shows lack of shell scripting knowledge, also @Shahbaz was kind enough to link to a description of all the "magic" which is just standard shell code

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