Use mode "r" for popen() in psql's evaluate_backtick().

In almost all other places, we use plain "r" or "w" mode in popen()
calls (the exceptions being for COPY data).  This one has been
overlooked (possibly because it's buried in a ".l" flex file?),
but it's using PG_BINARY_R.

Kensuke Okamura complained in bug #16688 that we fail to strip \r
when stripping the trailing newline from a backtick result string.
That's true enough, but we'd also fail to convert embedded \r\n
cleanly, which also seems undesirable.  Fixing the popen() mode
seems like the best way to deal with this.

It's been like this for a long time, so back-patch to all supported
branches.

Discussion: https://postgr.es/m/16688-c649c7b69cd7e6f8@postgresql.org

diff --git a/src/bin/psql/psqlscanslash.l b/src/bin/psql/psqlscanslash.l
index 2307491ba82c8561fca97b1bc74bf251a8274591..4dff84d6271a81b5282e1dbb630fdf0a437720da 100644 (file)
--- a/src/bin/psql/psqlscanslash.l
+++ b/src/bin/psql/psqlscanslash.l
@@ -777,7 +777,7 @@ evaluate_backtick(PsqlScanState state)
 
    initPQExpBuffer(&cmd_output);
 
-   fd = popen(cmd, PG_BINARY_R);
+   fd = popen(cmd, "r");
    if (!fd)
    {
        pg_log_error("%s: %m", cmd);
@@ -818,7 +818,7 @@ evaluate_backtick(PsqlScanState state)
    /* If no error, transfer result to output_buf */
    if (!error)
    {
-       /* strip any trailing newline */
+       /* strip any trailing newline (but only one) */
        if (cmd_output.len > 0 &&
            cmd_output.data[cmd_output.len - 1] == '\n')
            cmd_output.len--;