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syntax error in shell script

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# 1  
Old 07-31-2012
syntax error in shell script
I am creating a shell script. In which, I need to get server name and server IP. I used this command in script.
Code:
servername=`cat /etc/hosts|grep `eval hostname`|awk '{print $2}'`

however, when execute script or put set -x to debug, it return:
line 13: syntax error at line 13: `|' unexpected

I typed this line of command at command prompt, it works with exact server name returned. Please help me to identify where is the error. Thanks.
Last edited by duke0001; 07-31-2012 at 01:50 PM.. Reason: code tags
# 2  
Old 07-31-2012
Hi,

Try;

Code:
servername=`uname -n`

Regards

Dave
# 3  
Old 07-31-2012
You have doubly nested backtics - some shells have a problem with that try:
Code:
servername=$( cat /etc/hosts|grep `eval hostname`|awk '{print $2}' )

Also consider using nslookup, since not all server names will be in /etc/hosts
# 4  
Old 07-31-2012
gull04, jim:

Thanks so much for your prompt advise. I tested two commands. They are all work very well. I will use them. I chnaged my shell from
#!/bin/ksh to #!/bin/bash

My question remaining is, after I check and chnage my shell in script. It is Oracle Linux 5. So shell is bash shell. I used original script to test. it return this error code:

./script.sh: command substitution: line 13: syntax error near unexpected token `|'

It is pointed to the same error as begining. Why shell flavor has big difference?
# 5  
Old 07-31-2012
The big flavor difference is: you are depending on what is called undefined behavior.
POSIX standards no not say what happens with nested backtics, for example. So some nice guy who wrote shellA allows it to work correctly (correctly == your expectations, not really required to work). The evil guy who wrote shellB did not do that. He literally follows the standard

from opengroup.org (POSIX people):
Quote:
2.6.3 Command Substitution
Command substitution allows the output of a command to be substituted in place of the command name itself. Command substitution shall occur when the command is enclosed as follows:

$(command)


or (backquoted version):

`command`


The shell shall expand the command substitution by executing command in a subshell environment (see Shell Execution Environment ) and replacing the command substitution (the text of command plus the enclosing "$()" or backquotes) with the standard output of the command, removing sequences of one or more <newline> characters at the end of the substitution. Embedded <newline> characters before the end of the output shall not be removed; however, they may be treated as field delimiters and eliminated during field splitting, depending on the value of IFS and quoting that is in effect. If the output contains any null bytes, the behavior is unspecified.

Within the backquoted style of command substitution, <backslash> shall retain its literal meaning, except when followed by: '$' , '`' , or <backslash>. The search for the matching backquote shall be satisfied by the first unquoted non-escaped backquote; during this search, if a non-escaped backquote is encountered within a shell comment, a here-document, an embedded command substitution of the $( command) form, or a quoted string, undefined results occur. A single-quoted or double-quoted string that begins, but does not end, within the "`...`" sequence produces undefined results.

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