Bash变量内插，使用连字符或下划线分隔多个变量

Question

这是一个简单的脚本，只是为了查看文件是否已经下载。在此脚本中，即使未找到任何内容，find命令始终评估为零。因此我将其注释掉了。

在filename="day_CTRwFEES_hoo01M_"上，我不得不在文件名的末尾添加下划线。

使用下划线$filename_$yesterday.CSV来分隔两个变量无法正常工作。我必须将下划线删除，将其添加到文件名中，然后组合变量使其像这样工作 - $filename$yesterday。

我怎样才能使其在不添加下划线到$filename变量末尾的情况下正常工作？

#!/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

~

- capser

Answer 1

通过告诉bash变量名的结束位置。

"${filename}_$yesterday.CSV"

- Ignacio Vazquez-Abrams

---

在bash脚本中，始终使用${}来解释变量名称是一个好习惯。现在就开始做吧 :-) - Jan

Answer 2

有几种可能性：

• 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"
  

  or

  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"
  

（欢迎在本帖中添加其他方法。）

注：此句话是在提醒读者可以在这篇文章中自由地添加其他方法。

- gniourf_gniourf

Answer 3

你可以使用反斜杠来实现。

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

- Sriharsha Kalluru