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Top Forums UNIX for Advanced & Expert Users Linux expand dollar sign in single quotes Post 303042429 by rbatte1 on Tuesday 24th of December 2019 06:02:21 AM
Old 12-24-2019
Why single quotes anyway? They stop interpretation of the string quoted. If you want to pass something that changes, how about one of these:-
Code:
ssh $i "systemctl is-enabled ${j}";               # No quotes around the variable being passed
ssh $i "systemctl is-enabled '${j}'";             # Wraps single quotes around variable being passed, interpreted locally but not interpreted again remotely
ssh $i "systemctl is-enabled \"${j}\"";           # Wraps double quotes around variable being passed, interpreted locally but could then be interpreted again remotely if the variable is a remote variable name or subshell

The loops you have are rather badly structure too. I know that ssh will gobble up your input file with a normal while read line; do ssh user@server 'printf "Hello world\n"'; done < input_file but you can open multiple input files to help you. Would you consider:-
Code:
while read -u11 outer_variable                                            # Read from file descriptor 11
do
   while read -u12 inner_variable                                         # Read from file descriptor 12
   do
      ssh "${user}@${outer_variable}" "foo bar \"${inner_variable}\""
   done 12< "${inner_variable_input_file}"                                # Supply input file on file descriptor 12
done 11< "${outer_variable_input_file}"                                   # Supply input file on file descriptor 11

Obviously it's better to use meaningful variable names. It avoids confusion from re-using them, breaking something that calls your code but has the same names and means you can understand your code when you come back to it many years later. Using i or j might save a few characters typing, but will be worse in the long run.



I hope that these help,
Robin
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atexpand(3)						       AtFS Toolkit Library						       atexpand(3)

NAME
atExpandAttrs, atExpand - attribute expansion SYNOPSIS
#include <atfs.h> #include <atfstk.h> int atExpandAttrs (Af_key *aso, char *buf, size_t bufSize, FILE *dest, size_t destSize, int mode); int atExpand; DESCRIPTION
atExpandAttrs scans the char buffer buf to the extent of bufSize for strings of the form $__attributeName optionally followed by a delimit- ing (second) dollar sign ($). If such a string is found, the buffer contents up to the character preceding the first dollar sign will be sent to the destination output dest. If an attribute with name attributeName is set for the current attributed software object aso, the citation-string will be substituted by the value of that attribute and appended to the output. Output of buf contents resumes with the first character after the whitespace character or dollar sign delimiting attributeName. Despite the type of the dest argument (pointer to file structure), atExpandAttrs may be caused to copy it's output to a string buffer rather than an open file. In this case, the constant AT_EXPAND_STRING must be given as mode argument and bufSize must be set to indicate the length of the destination buffer dest (will be casted to character pointer). If destSize is to small to hold the result string, atEx- pandAttrs returns a negative value. In the regular case, where output shall be written to a file, the mode parameter must be AT_EXPAND_FILE. The atExpand variable suppresses attribute expansion when set FALSE. The variable may be set either directly from the application program if indirectly by evaluation of the pseudo attribute citation $__xpoff in any buffer scanned by atExpandAttrs. Another pseudo attribute citation $__xpon cancels the effect of a previous $__xpoff and switches attribute citation on again. It does not, however, enable attribute citation if this was disabled explicitly by the application program. DIAGNOSTICS
atExpandAttrs returns -1 on error. Additionally, the atError variable is set and afErrMsg holds a diagnostic message. SEE ALSO
atattribute(3) AtFStk-1.12 Fri Jun 25 16:39:36 1993 atexpand(3)
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