使用Sed在Bash脚本中搜索/替换变量

Question

I'm trying to change the date in the first line of a text file by using Sed to replace the previous days date with the current days date.

Below is the code from the bash script that I'm trying to use to accomplish this:

YMD=$(date +%Y%m%d)

ODA=$(date -u +%Y%m%d --date="1 days ago")

mv ${HOMEDIR}/${PATH1}/nws_${VAR}_conus_daily_${ODA}.ctl ${HOMEDIR}/${PATH1}/nws_${VAR}_conus_daily_${YMD}.ctl

sed "s/${ODA}/${YMD}/" ${HOMEDIR}/${PATH1}/nws_${VAR}_conus_daily_${YMD}.ctl

URL1=http://water.weather.gov/${VAR}/p_download_new/${Y}/${M}/${D}/nws_${VAR}_conus_${YMD}.nc

wget -P ${HOMEDIR}/${PATH1}/ -N ${URL1}

The first line in the text file reads as follows:

dset ^grads/data/ahps/nws_precip_conus_20140423.nc

Answer 1

If you want sed to change your file, you have to give the -i option, like so:

sed -i "s/${ODA}/${YMD}/" ${HOMEDIR}/${PATH1}/nws_${VAR}_conus_daily_${YMD}.ctl

Otherwise sed will just output the changed file to standard output.

Answer 2

Use this:

sed "1s/[0-9]\+\.nc/$(date +%Y%m%d).nc/" file.txt

It replace the numbers before .nc in the first line of file.txt with the output of

date +%Y%m%d

which outputs the current date in the desired format.

---

Proof of functionality :

Having file.txt as this:

dset ^grads/data/ahps/nws_precip_conus_20140421.nc
bla bla 20140421.nc

Issue the above command:

sed "1s/[0-9]\+\.nc/$(date +%Y%m%d).nc/" file.txt

Output:

dset ^grads/data/ahps/nws_precip_conus_20140423.nc
bla bla 20140421.nc

You see that the date in the first line and only that has been replaced by the current date.