Replacing error redirection to null device in Bash script and create a new file

Question

I am attempting to create a new debug installation script from an existing one. The original installation script contains many statements with redirection >/dev/null 2>&1 . It includes different patterns so I found the regex expression that matches all:

>{1,2}\s{0,1}\/dev\/null 2>\&1

I've tested this regex here .

Now I'd like to use this pattern to find and replace all instances of matches with a blank so that in case there are any errors, the output stream will be redirected to the terminal rather to the null device. My attempt is:

sed 's+>{1,2}\s\/dev\/null 2>\&1++g' install.sh > install_debug.sh

(I used the + instead of / as the delimiter to make the string more readable)

But when I grep the output file or just pipe the output without creating the file, /dev/null shows that the substitution was not successful:

sed 's/>{1,2}\s\/dev\/null 2>\&1//g' install.sh | grep "null"
  elif type lsb_release >/dev/null 2>&1; then
    if lsof /var/lib/dpkg/lock >> /dev/null 2>&1; then
      sudo apt-get update > /dev/null 2>&1 && \
      sudo DEBIAN_FRONTEND=falseninteractive apt-get install -y sshpass python-minimal python-pip dbus > /dev/null 2>&1 && \
      sudo apt-get install -y jq > /dev/null 2>&1
      sudo python_for_core_os > /dev/null 2>&1

Any ideas what I'm doing wrong?

Thanks!

Answer 1

You are having \s in an attempt to match 1 or more between > and /dev , but the strings can have more or none. Besides, you are not escaping braces in the POSIX BRE pattern, so sed 's/a{1,2}//' effectively removes the first a{1,2} text, not one or two a s. Either use a POSIX ERE (with the -E option) to use a{1,2} , or escape the braces (ie sed -E 's/a{1,2}//' = sed 's/a\{1,2\}//' ).

Also, & in the regex pattern is not special, it is only special in the replacement part. Thus, no need escaping it here. Also, since you used + as a delimiter, there is no point escaping / chars any longer, replace \/ with / .

Use

sed 's+>\{1,2\}[[:space:]]*/dev/null[[:space:]]*2>&1++g' install.sh > install_debug.sh

In a GNU sed you may surely use \s to shorten the pattern:

sed -E 's+>{1,2}\s*/dev/null\s*2>&1++g' install.sh > install_debug.sh

See the online sed demo

Answer 2

You have to escape the { :

$ sed 's#>\{1,2\}\s*/dev/null\s*2>\&1##g' install.txt
  elif type lsb_release ; then
    if lsof /var/lib/dpkg/lock ; then
      sudo apt-get update  && \
      sudo DEBIAN_FRONTEND=falseninteractive apt-get install -y sshpass python-minimal python-pip dbus  && \
      sudo apt-get install -y jq 
      sudo python_for_core_os