| 1 | #!/usr/bin/env bash
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| 2 | #
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| 3 | # Prep for the "Ultimate Guide to errexit".
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| 4 | #
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| 5 | # Usage:
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| 6 | # ./errexit-pitfalls.sh <function name>
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| 7 |
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| 8 | set -o nounset
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| 9 | set -o pipefail
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| 10 | set -o errexit
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| 11 |
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| 12 | die() {
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| 13 | echo "$@" >&2
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| 14 | exit 1
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| 15 | }
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| 16 |
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| 17 | #
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| 18 | # inherit_errexit (bash and Oil)
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| 19 | #
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| 20 | # It's confusing that command subs clear the errexit flag (but subshells
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| 21 | # don't.)
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| 22 |
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| 23 | # This is a bash quirk
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| 24 | command-sub-needs-inherit-errexit() {
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| 25 | echo $(echo 1; false; echo 2)
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| 26 |
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| 27 | echo 'inherit_errexit'
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| 28 | shopt -s inherit_errexit || die "bash 4.4 required"
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| 29 |
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| 30 | echo $(echo 1; false; echo 2)
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| 31 | }
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| 32 |
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| 33 | subshell-demo() {
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| 34 | ( echo 1; false; echo 2 ) # prints 1
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| 35 | }
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| 36 |
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| 37 | #
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| 38 | # command_sub_errexit (Oil)
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| 39 | #
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| 40 | # It's confusing that a=$(false) is different than local a=$(false).
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| 41 |
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| 42 | assignment-builtin-overwrites-status() {
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| 43 | set +o errexit
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| 44 |
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| 45 | a=$(false)
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| 46 | echo $? # this is 1
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| 47 |
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| 48 | local b=$(false)
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| 49 | echo $? # surprisingly, it's 0!
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| 50 | }
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| 51 |
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| 52 | oil-more-errexit() {
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| 53 | shopt -s command_sub_errexit
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| 54 |
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| 55 | local b=$(false) # FAILS!
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| 56 | echo $?
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| 57 | }
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| 58 |
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| 59 | #
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| 60 | # strict_errexit (Oil)
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| 61 | #
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| 62 | # It's confusing that 'if myfunc', 'while/until myfunc', 'myfunc || die',
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| 63 | # 'myfunc && echo OK' and '! myfunc' change errexit.
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| 64 |
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| 65 | myfunc() {
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| 66 | echo '--- myfunc'
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| 67 | ls /zz # should cause failure
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| 68 | echo "shouldn't get here"
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| 69 | }
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| 70 |
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| 71 | proper-function-failure() {
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| 72 | # Proper failure
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| 73 | myfunc
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| 74 | echo "Doesn't get here"
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| 75 | }
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| 76 |
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| 77 | # Function calls in condition cause the function to IGNORE FAILURES
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| 78 | function-call-in-condition() {
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| 79 | # All 4 of these surprisingly don't fail
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| 80 |
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| 81 | if myfunc; then
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| 82 | echo 'if'
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| 83 | fi
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| 84 |
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| 85 | myfunc && echo '&&'
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| 86 |
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| 87 | myfunc || echo 'not printed'
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| 88 |
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| 89 | ! myfunc
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| 90 | }
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| 91 |
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| 92 | proper-lastpipe-failure() {
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| 93 | { echo hi; exit 5; } | sort
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| 94 | echo "doesn't get here"
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| 95 | }
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| 96 |
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| 97 | # Same problem for pipelines, another compound command.
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| 98 | pipeline-in-conditionals() {
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| 99 | # If the above function aborts early, then this one should too.
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| 100 | if { echo hi; exit 5; } | sort; then
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| 101 | echo true
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| 102 | else
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| 103 | echo false
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| 104 | fi
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| 105 | echo bad
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| 106 | }
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| 107 |
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| 108 | #
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| 109 | # Conditional As Last Statement in Function Pitfall
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| 110 | #
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| 111 | # It's confusing that calling a one-line function with 'foo && echo OK' isn't
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| 112 | # the same as inlining that statement (due to differing exit codes).
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| 113 |
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| 114 |
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| 115 | # Possible strict_errexit rule:
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| 116 | # Disallow && (an AndOr with && as one of the operators) unless it's in an
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| 117 | # if/while/until condition.
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| 118 | # This would require an extra flag for _Execute().
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| 119 | # cmd_flags | ERREXIT (to avoid the stack)
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| 120 | # cmd_flags | IS_CONDITION
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| 121 |
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| 122 | last-func() {
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| 123 | test -d nosuchdir && echo no dir
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| 124 | echo survived
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| 125 |
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| 126 | set -e
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| 127 | f() { test -d nosuchdir && echo no dir; }
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| 128 | echo 'in function'
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| 129 | f
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| 130 |
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| 131 | # We do NOT get here.
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| 132 | echo survived
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| 133 | }
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| 134 |
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| 135 |
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| 136 | #
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| 137 | # Builtins
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| 138 | #
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| 139 |
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| 140 | read-exit-status() {
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| 141 | set +o errexit
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| 142 |
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| 143 | echo line > _tmp/line
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| 144 | read x < _tmp/line # status 0 as expected
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| 145 | echo status=$?
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| 146 |
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| 147 | echo -n no-newline > _tmp/no
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| 148 | read x < _tmp/no # somewhat surprising status 1, because no delimiter read
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| 149 | # This is for terminating loops?
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| 150 |
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| 151 | echo status=$?
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| 152 |
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| 153 | # Solution: Oil can have its own builtin. It already has 'getline'.
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| 154 | # getfile / slurp / readall
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| 155 | # readall :x < myfile
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| 156 | #
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| 157 | # grep foo *.c | readall :results
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| 158 | #
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| 159 | # grep foo *.c | slurp :results # I Kind of like this
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| 160 | #
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| 161 | # Unlike $(echo hi), it includes the newline
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| 162 | # Unlike read x, it doesn't fail if there's NO newline.
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| 163 | }
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| 164 |
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| 165 |
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| 166 | #
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| 167 | # lastpipe and SIGPIPE
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| 168 | #
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| 169 |
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| 170 | # This is a bit of trivia about the exit status.
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| 171 | sigpipe-error() {
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| 172 | set +o errexit
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| 173 | busybox | head -n 1
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| 174 | echo status=$? # 141 because of sigpipe
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| 175 |
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| 176 | # Workaround
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| 177 | { busybox || true; } | head -n 1
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| 178 | echo status=$?
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| 179 | }
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| 180 |
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| 181 | #
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| 182 | # Other constructs I don't care about from https://mywiki.wooledge.org/BashFAQ/105
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| 183 | #
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| 184 |
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| 185 | #
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| 186 | # - let i++
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| 187 | # - (( i++ ))
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| 188 |
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| 189 | # So we DO want command_sub_errexit. Because we don't want
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| 190 | #
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| 191 | # diff $(error 1) $(error 2)
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| 192 | #
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| 193 | # to execute the diff! It should fail earlier
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| 194 |
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| 195 | word-failures() {
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| 196 | set -o errexit
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| 197 |
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| 198 | echo $BASH_VERSION
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| 199 | #shopt -s inherit_errexit
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| 200 |
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| 201 | echo "command sub $(false)"
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| 202 | echo status=$?
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| 203 |
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| 204 | readonly x="readonly command sub $(false)"
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| 205 | echo status=$?
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| 206 |
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| 207 | [[ "dparen $(false)" == 'dparen ' ]]
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| 208 | echo status=$?
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| 209 |
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| 210 | (( a = $(false)42 ))
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| 211 | echo status=$?
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| 212 | echo a=$a
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| 213 |
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| 214 | diff -u <(cat nonexistent.txt) /dev/null
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| 215 | echo status=$?
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| 216 | }
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| 217 |
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| 218 | "$@"
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| 219 |
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