Trouble swapping datestamps in a log file's name using Bash

Question

I'm trying to swap the date in a log file's name using a bash script. I cannot seem to get the date's to play nice however.

When I try to swap the dates using sed, the original date is still in the filename (I'm echoing instead of using mv for now):

#!/bin/bash
DATE=`date +%Y-%m-%d`
YESTERDATE= date -d 'yesterday 13:00' '+%Y-%m-%d'
echo "$DATE"
echo "$YESTERDATE"
for LOGFILE in *.$DATE;
do
    newfile="$(echo ${LOGFILE} |sed -e 's/$DATE/$YESTERDATE/')" ;
    echo "$newfile"
    #mv -- "$LOGFILE" "$newfile";
done

The log files I want changed are only the ones with todays date in them. The format is log_file.log.2018-07-17. I want it to be changed to log_file.log.2018-07-16.

Is the issue with how I am using variable names in the sed command?

I think Sundeep is correct, the single quotes are preventing the variable expansion for DATE and YESTERDATE. Change that line as Sundeep has suggested: newfile="$(echo ${LOGFILE} |sed -e "s/$DATE/$YESTERDATE/")" with $() the nested quotes will be fine. — Kyle Burton, Jul 17 '18 at 14:31
Replace `YESTERDATE= date -d 'yesterday 13:00' '+%Y-%m-%d'` with `YESTERDATE="$(date -d 'yesterday 13:00' '+%Y-%m-%d')"` — Inian, Jul 17 '18 at 14:33
See http://rextester.com/LHNH4768. Inian is right, the `$YESTERDATE` variable is empty when inside `for` loop if you do not place its definition inside `"$()"`. — Wiktor Stribiżew, Jul 17 '18 at 14:35
The tool `sed` is dated. A lot of features are missing in this tool. Why not use a modern scripting language? — guettli, Jul 17 '18 at 14:38

score 1 · Accepted Answer · answered Jul 17 '18 at 14:34

1

You have a problem with quoting. This line

newfile="$(echo ${LOGFILE} |sed -e 's/$DATE/$YESTERDATE/')"

uses single quotes for the sed - and single quotes prevent the variables being substituted. You'll see the problem if you try something simple like

echo "$(echo '$foo')"

Instead, try

newfile=$(echo ${LOGFILE} |sed -e "s/$DATE/$YESTERDATE/")

answered Jul 17 '18 at 14:34

Jon

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That is indeed correct! I guess I need to brush up on my Bash syntax. Thank you! – GreenGodot Jul 17 '18 at 14:40
In addition, you need to use double quotes around `$LOGFILE` everywhere. The curly braces are not necessary or useful. – tripleee Jul 17 '18 at 16:48

score 0 · Answer 2 · answered Jul 17 '18 at 14:35

One thing it's "", second it's bad YESTERDATE try to echo it. For me working something like this:

#!/bin/bash
DATE=`date +%Y-%m-%d`
#change No.1
YESTERDATE=$(date -d 'yesterday 13:00' '+%Y-%m-%d')
echo "$DATE"
echo "$YESTERDATE"
for LOGFILE in *.$DATE;
do
    #change No.2
    newfile="$(echo ${LOGFILE} |sed -e "s/$DATE/$YESTERDATE/")" ;
    echo "$newfile"
    #mv -- "$LOGFILE" "$newfile";
done

score 0 · Answer 3 · answered Jul 17 '18 at 14:36

0

Hi modify below line in your script like :-

 newfile=$(echo ${LOGFILE} | sed -e 's/'$DATE'/'$YESTERDATE'/')

in sed, string variable should be under single quote '

answered Jul 17 '18 at 14:36

Abhijit Pritam Dutta

5,010
2
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Trouble swapping datestamps in a log file's name using Bash

3 Answers3