bash variable interpolation separate variables by a hyphen or underscore

问题

This is a simple script just to see if the file has been downloaded. On this script the find command always evaluated to zero - even if it didn\'t find anything. So I commented it out.

on the filename=\"day_CTRwFEES_hoo01M_\" I had to add an underscore to the end of the filename.

Using an underscore $filename_$yesterday.CSV to separate the two did not work. - I had to take out the underscore, add it to the filename and then combine the variables to make it work like this - $filename$yesterday.

How could I get it to work without adding the underscore to the end of the variable $filename?

#!/bin/bash
set -x
dayofweek=$(/bin/date +%w)
today=$(/bin/date +%Y%m%d)
yesterday=$(/bin/date -d \"1 day ago\" +%Y%m%d)
friday_morning=$(/bin/date -d \"3 days ago\" +%Y%m%d)
filename=\"day_CTRwFEES_hoo01M_\"

#if find /data/today/ -type f -name \"$filename_$yesterday.CSV\" ; then
if ls \"/data/today/$filename$yesterday.CSV\" ; then
    echo \"successful\"
else
    echo \"$filename$yesterday.CSV was not downloaded, please check.\" | mail -s \"$filename$yesterday.CSV not downloaded\" casper@big_bank.com
    fi

casper@good_host5981dap:~/walt/morning_checks$ ./check_day_CTRwFEES_hoo01M
++ /bin/date +%w
+ dayofweek=5
++ /bin/date +%Y%m%d
+ today=20141024
++ /bin/date -d \'1 day ago\' +%Y%m%d
+ yesterday=20141023
++ /bin/date -d \'3 days ago\' +%Y%m%d
+ friday_morning=20141021
+ filename=day_CTRwFEES_hoo01M_
+ ls data/today/day_CTRwFEES_hoo01M_20141023.CSV
/data/today/day_CTRwFEES_hoo01M_20141023.CSV
+ echo successful
successful

回答1:

By telling bash where the variable name ends.

"${filename}_$yesterday.CSV"

回答2:

Several possibilities:

The most natural one: enclose your variable name in curly brackets (Ignacio Vazquez-Abrams's solution):
```
echo "${filename}_$yesterday.CSV"
```
Since your separator is a rather special character, you may use a backslash (Sriharsha's Kallury's solution):
```
echo "$filename\_$yesterday.CSV"
```

(Ab)use quotes:

echo "$filename""_$yesterday.CSV"

echo "$filename"_"$yesterday.CSV"

Use an auxiliary variable for the separator:
```
sep=_
echo "$filename$sep$yesterday.CSV"
```

Use an auxiliary variable for the final string, and build it step by step:

final=$filename
final+=_$yesterday.CSV
echo "$final"

or in a longer fashion:

final=$filename
final+=_
final+=$yesterday
final+=.CSV
echo "$final"

Use an auxiliary variable for the final string, and build it with printf:
```
printf -v final "%s_%s.CSV" "$filename" "$yesterday"
echo "$final"
```

(feel free to add other methods to this post).

回答3:

You can use backslash to do that.

# filename=test
# yesterday=somedate
# echo $filename_$yesterday.csv
somedate.csv
# echo $filename\_$yesterday.csv
test_somedate.csv
#

来源：https://stackoverflow.com/questions/26559617/bash-variable-interpolation-separate-variables-by-a-hyphen-or-underscore

标签

bash

variables

string-interpolation